VMware ESXI - 6.0.1 User Manual

vSphere Resource Management

Update 1

ESXi 6.0

vCenter Server 6.0

This document supports the version of each product listed and supports all subsequent versions until the document is replaced by a new edition. To check for more recent editions of this document, see http://www.vmware.com/support/pubs.

EN-001903-01

vSphere Resource Management

You can find the most up-to-date technical documentation on the VMware Web site at:

http://www.vmware.com/support/

The VMware Web site also provides the latest product updates.

If you have comments about this documentation, submit your feedback to:

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About vSphere Resource Management 7

Updated Information 9

Getting Started with Resource Management 11

Resource Types 11

Resource Providers 11

Resource Consumers 12

Goals of Resource Management 12

Configuring Resource Allocation Settings 13

Resource Allocation Shares 13

Resource Allocation Reservation 14

Resource Allocation Limit 14

Resource Allocation Settings Suggestions 15

Edit Resource Settings 15

Changing Resource Allocation Settings—Example 16

Admission Control 17

CPU Virtualization Basics 19

Software-Based CPU Virtualization 19

Hardware-Assisted CPU Virtualization 20

Virtualization and Processor-Specific Behavior 20

Performance Implications of CPU Virtualization 20

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Administering CPU Resources 21

View Processor Information 21

Specifying CPU Configuration 21

Multicore Processors 22

Hyperthreading 22

Using CPU Affinity 24

Host Power Management Policies 25

Memory Virtualization Basics 29

Virtual Machine Memory 29

Memory Overcommitment 30

Memory Sharing 30

Types of Memory Virtualization 31

Administering Memory Resources 35

Understanding Memory Overhead 35

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How ESXi Hosts Allocate Memory 36

Memory Reclamation 37

Using Swap Files 38

Sharing Memory Across Virtual Machines 42

Memory Compression 43

Measuring and Differentiating Types of Memory Usage 44

Memory Reliability 45

About System Swap 45

View Graphics Information 47

Managing Storage I/O Resources 49

Storage I/O Control Requirements 49

Storage I/O Control Resource Shares and Limits 50

Set Storage I/O Control Resource Shares and Limits 51

Enable Storage I/O Control 51

Set Storage I/O Control Threshold Value 52

Storage DRS Integration with Storage Profiles 53

Managing Resource Pools 55

Why Use Resource Pools? 56

Create a Resource Pool 57

Edit a Resource Pool 58

Add a Virtual Machine to a Resource Pool 58

Remove a Virtual Machine from a Resource Pool 59

Remove a Resource Pool 60

Resource Pool Admission Control 60

Creating a DRS Cluster 63

Admission Control and Initial Placement 64

Virtual Machine Migration 65

DRS Cluster Requirements 67

Configuring DRS with Virtual Flash 68

Create a Cluster 68

Edit a Cluster 69

Create a DRS Cluster 70

Set a Custom Automation Level for a Virtual Machine 71

Disable DRS 72

Restore a Resource Pool Tree 72

Using DRS Clusters to Manage Resources 73

Adding Hosts to a Cluster 73

Adding Virtual Machines to a Cluster 75

Removing Virtual Machines from a Cluster 75

Removing a Host from a Cluster 76

DRS Cluster Validity 77

Managing Power Resources 82

Using DRS Affinity Rules 86

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Contents

Creating a Datastore Cluster 91

Initial Placement and Ongoing Balancing 92

Storage Migration Recommendations 92

Create a Datastore Cluster 92

Enable and Disable Storage DRS 93

Set the Automation Level for Datastore Clusters 93

Setting the Aggressiveness Level for Storage DRS 94

Datastore Cluster Requirements 95

Adding and Removing Datastores from a Datastore Cluster 96

Using Datastore Clusters to Manage Storage Resources 97

Using Storage DRS Maintenance Mode 97

Applying Storage DRS Recommendations 99

Change Storage DRS Automation Level for a Virtual Machine 100

Set Up Off-Hours Scheduling for Storage DRS 100

Storage DRS Anti-Affinity Rules 101

Clear Storage DRS Statistics 104

Storage vMotion Compatibility with Datastore Clusters 105

Using NUMA Systems with ESXi 107

What is NUMA? 107

How ESXi NUMA Scheduling Works 108

VMware NUMA Optimization Algorithms and Settings 109

Resource Management in NUMA Architectures 110

Using Virtual NUMA 110

Specifying NUMA Controls 112

Advanced Attributes 115

Set Advanced Host Attributes 115

Set Advanced Virtual Machine Attributes 118

Latency Sensitivity 120

About Reliable Memory 120

Fault Definitions 123

Virtual Machine is Pinned 124

Virtual Machine not Compatible with any Host 124

VM/VM DRS Rule Violated when Moving to another Host 124

Host Incompatible with Virtual Machine 124

Host has Virtual Machine that Violates VM/VM DRS Rules 124

Host has Insufficient Capacity for Virtual Machine 124

Host in Incorrect State 124

Host has Insufficient Number of Physical CPUs for Virtual Machine 125

Host has Insufficient Capacity for Each Virtual Machine CPU 125

The Virtual Machine is in vMotion 125

No Active Host in Cluster 125

Insufficient Resources 125

Insufficient Resources to Satisfy Configured Failover Level for HA 125

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No Compatible Hard Affinity Host 125

No Compatible Soft Affinity Host 125

Soft Rule Violation Correction Disallowed 125

Soft Rule Violation Correction Impact 126

DRS Troubleshooting Information 127

Cluster Problems 127

Host Problems 130

Virtual Machine Problems 133

Index 137

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About vSphere Resource Management

vSphere Resource Management describes resource management for VMware® ESXi and vCenter® Server environments.

This documentation focuses on the following topics.

Resource allocation and resource management concepts

Virtual machine attributes and admission control

Resource pools and how to manage them

Clusters, vSphere® Distributed Resource Scheduler (DRS), vSphere Distributed Power Management

(DPM), and how to work with them

Datastore clusters, Storage DRS, Storage I/O Control, and how to work with them

Advanced resource management options

Performance considerations

Intended Audience

This information is for system administrators who want to understand how the system manages resources and how they can customize the default behavior. It’s also essential for anyone who wants to understand and use resource pools, clusters, DRS, datastore clusters, Storage DRS, Storage I/O Control, or vSphere DPM.

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This documentation assumes you have a working knowledge of VMware ESXi and of vCenter Server.

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Updated Information

This vSphere Resource Management is updated with each release of the product or when necessary.

This table provides the update history of the vSphere Resource Management.

Revision Description

001903-01

001903-00 Initial release.

Added “Storage DRS Integration with Storage Profiles,” on page 53.

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Getting Started with Resource

Management 1

To understand resource management, you must be aware of its components, its goals, and how best to implement it in a cluster setting.

Resource allocation settings for a virtual machine (shares, reservation, and limit) are discussed, including how to set them and how to view them. Also, admission control, the process whereby resource allocation settings are validated against existing resources is explained.

Resource management is the allocation of resources from resource providers to resource consumers.

The need for resource management arises from the overcommitment of resources—that is, more demand than capacity and from the fact that demand and capacity vary over time. Resource management allows you to dynamically reallocate resources, so that you can more efficiently use available capacity.

This chapter includes the following topics:

“Resource Types,” on page 11

“Resource Providers,” on page 11

“Resource Consumers,” on page 12

“Goals of Resource Management,” on page 12

Resource Types

Resources include CPU, memory, power, storage, and network resources.

NOTE ESXi manages network bandwidth and disk resources on a per-host basis, using network traffic shaping and a proportional share mechanism, respectively.

Resource Providers

Hosts and clusters, including datastore clusters, are providers of physical resources.

For hosts, available resources are the host’s hardware specification, minus the resources used by the virtualization software.

A cluster is a group of hosts. You can create a cluster using vSphere Web Client, and add multiple hosts to the cluster. vCenter Server manages these hosts’ resources jointly: the cluster owns all of the CPU and memory of all hosts. You can enable the cluster for joint load balancing or failover. See Chapter 10,

“Creating a DRS Cluster,” on page 63 for more information.

A datastore cluster is a group of datastores. Like DRS clusters, you can create a datastore cluster using the vSphere Web Client, and add multiple datstores to the cluster. vCenter Server manages the datastore resources jointly. You can enable Storage DRS to balance I/O load and space utilization. See Chapter 12,

“Creating a Datastore Cluster,” on page 91.

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Resource Consumers

Virtual machines are resource consumers.

The default resource settings assigned during creation work well for most machines. You can later edit the virtual machine settings to allocate a share-based percentage of the total CPU, memory, and storage I/O of the resource provider or a guaranteed reservation of CPU and memory. When you power on that virtual machine, the server checks whether enough unreserved resources are available and allows power on only if there are enough resources. This process is called admission control.

A resource pool is a logical abstraction for flexible management of resources. Resource pools can be grouped into hierarchies and used to hierarchically partition available CPU and memory resources. Accordingly, resource pools can be considered both resource providers and consumers. They provide resources to child resource pools and virtual machines, but are also resource consumers because they consume their parents’ resources. See Chapter 9, “Managing Resource Pools,” on page 55.

ESXi hosts allocate each virtual machine a portion of the underlying hardware resources based on a number of factors:

Resource limits defined by the user.

Total available resources for the ESXi host (or the cluster).

Number of virtual machines powered on and resource usage by those virtual machines.

Overhead required to manage the virtualization.

Goals of Resource Management

When managing your resources, you should be aware of what your goals are.

In addition to resolving resource overcommitment, resource management can help you accomplish the following:

Performance Isolation—prevent virtual machines from monopolizing resources and guarantee

predictable service rates.

Efficient Utilization—exploit undercommitted resources and overcommit with graceful degradation.

Easy Administration—control the relative importance of virtual machines, provide flexible dynamic

partitioning, and meet absolute service-level agreements.

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Configuring Resource Allocation

Settings 2

When available resource capacity does not meet the demands of the resource consumers (and virtualization overhead), administrators might need to customize the amount of resources that are allocated to virtual machines or to the resource pools in which they reside.

Use the resource allocation settings (shares, reservation, and limit) to determine the amount of CPU, memory, and storage resources provided for a virtual machine. In particular, administrators have several options for allocating resources.

Reserve the physical resources of the host or cluster.

Set an upper bound on the resources that can be allocated to a virtual machine.

Guarantee that a particular virtual machine is always allocated a higher percentage of the physical

resources than other virtual machines.

This chapter includes the following topics:

“Resource Allocation Shares,” on page 13

“Resource Allocation Reservation,” on page 14

“Resource Allocation Limit,” on page 14

“Resource Allocation Settings Suggestions,” on page 15

“Edit Resource Settings,” on page 15

“Changing Resource Allocation Settings—Example,” on page 16

“Admission Control,” on page 17

Resource Allocation Shares

Shares specify the relative importance of a virtual machine (or resource pool). If a virtual machine has twice as many shares of a resource as another virtual machine, it is entitled to consume twice as much of that resource when these two virtual machines are competing for resources.

Shares are typically specified as High, Normal, or Low and these values specify share values with a 4:2:1 ratio, respectively. You can also select Custom to assign a specific number of shares (which expresses a proportional weight) to each virtual machine.

Specifying shares makes sense only with regard to sibling virtual machines or resource pools, that is, virtual machines or resource pools with the same parent in the resource pool hierarchy. Siblings share resources according to their relative share values, bounded by the reservation and limit. When you assign shares to a virtual machine, you always specify the priority for that virtual machine relative to other powered-on virtual machines.

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The following table shows the default CPU and memory share values for a virtual machine. For resource pools, the default CPU and memory share values are the same, but must be multiplied as if the resource pool were a virtual machine with four virtual CPUs and 16 GB of memory.

Table 2‑1. Share Values

Setting CPU share values Memory share values

High 2000 shares per virtual CPU 20 shares per megabyte of configured virtual

Normal 1000 shares per virtual CPU 10 shares per megabyte of configured virtual

Low 500 shares per virtual CPU 5 shares per megabyte of configured virtual machine

For example, an SMP virtual machine with two virtual CPUs and 1GB RAM with CPU and memory shares set to Normal has 2x1000=2000 shares of CPU and 10x1024=10240 shares of memory.

NOTE Virtual machines with more than one virtual CPU are called SMP (symmetric multiprocessing) virtual machines. ESXi supports up to 128 virtual CPUs per virtual machine.

The relative priority represented by each share changes when a new virtual machine is powered on. This affects all virtual machines in the same resource pool. All of the virtual machines have the same number of virtual CPUs. Consider the following examples.

machine memory.

memory.

Two CPU-bound virtual machines run on a host with 8GHz of aggregate CPU capacity. Their CPU

shares are set to Normal and get 4GHz each.

A third CPU-bound virtual machine is powered on. Its CPU shares value is set to High, which means it

should have twice as many shares as the machines set to Normal. The new virtual machine receives 4GHz and the two other machines get only 2GHz each. The same result occurs if the user specifies a custom share value of 2000 for the third virtual machine.

Resource Allocation Reservation

A reservation specifies the guaranteed minimum allocation for a virtual machine.

vCenter Server or ESXi allows you to power on a virtual machine only if there are enough unreserved resources to satisfy the reservation of the virtual machine. The server guarantees that amount even when the physical server is heavily loaded. The reservation is expressed in concrete units (megahertz or megabytes).

For example, assume you have 2GHz available and specify a reservation of 1GHz for VM1 and 1GHz for VM2. Now each virtual machine is guaranteed to get 1GHz if it needs it. However, if VM1 is using only 500MHz, VM2 can use 1.5GHz.

Reservation defaults to 0. You can specify a reservation if you need to guarantee that the minimum required amounts of CPU or memory are always available for the virtual machine.

Resource Allocation Limit

Limit specifies an upper bound for CPU, memory, or storage I/O resources that can be allocated to a virtual machine.

A server can allocate more than the reservation to a virtual machine, but never allocates more than the limit, even if there are unused resources on the system. The limit is expressed in concrete units (megahertz, megabytes, or I/O operations per second).

CPU, memory, and storage I/O resource limits default to unlimited. When the memory limit is unlimited, the amount of memory configured for the virtual machine when it was created becomes its effective limit.

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In most cases, it is not necessary to specify a limit. There are benefits and drawbacks:

Benefits — Assigning a limit is useful if you start with a small number of virtual machines and want to

manage user expectations. Performance deteriorates as you add more virtual machines. You can simulate having fewer resources available by specifying a limit.

Drawbacks — You might waste idle resources if you specify a limit. The system does not allow virtual

machines to use more resources than the limit, even when the system is underutilized and idle resources are available. Specify the limit only if you have good reasons for doing so.

Resource Allocation Settings Suggestions

Select resource allocation settings (reservation, limit and shares) that are appropriate for your ESXi environment.

The following guidelines can help you achieve better performance for your virtual machines.

Use Reservation to specify the minimum acceptable amount of CPU or memory, not the amount you

want to have available. The amount of concrete resources represented by a reservation does not change when you change the environment, such as by adding or removing virtual machines. The host assigns additional resources as available based on the limit for your virtual machine, the number of shares and estimated demand.

When specifying the reservations for virtual machines, do not commit all resources (plan to leave at

least 10% unreserved). As you move closer to fully reserving all capacity in the system, it becomes increasingly difficult to make changes to reservations and to the resource pool hierarchy without violating admission control. In a DRS-enabled cluster, reservations that fully commit the capacity of the cluster or of individual hosts in the cluster can prevent DRS from migrating virtual machines between hosts.

Chapter 2 Configuring Resource Allocation Settings

If you expect frequent changes to the total available resources, use Shares to allocate resources fairly

across virtual machines. If you use Shares, and you upgrade the host, for example, each virtual machine stays at the same priority (keeps the same number of shares) even though each share represents a larger amount of memory, CPU, or storage I/O resources.

Edit Resource Settings

Use the Edit Resource Settings dialog box to change allocations for memory and CPU resources.

Procedure

1 Browse to the virtual machine in the vSphere Web Client navigator.

2 Right-click and select Edit Resource Settings.

3 Edit the CPU Resources.

Option Description

Reservation

Limit

CPU shares for this resource pool with respect to the parent’s total. Sibling resource pools share resources according to their relative share values bounded by the reservation and limit. Select Low, Normal, or High, which specify share values respectively in a 1:2:4 ratio. Select Custom to give each virtual machine a specific number of shares, which expresses a proportional weight.

Guaranteed CPU allocation for this resource pool.

Upper limit for this resource pool’s CPU allocation. Select Unlimited to specify no upper limit.

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VM-QA

host

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4 Edit the Memory Resources.

Option Description

Reservation

Limit

Memory shares for this resource pool with respect to the parent’s total. Sibling resource pools share resources according to their relative share values bounded by the reservation and limit. Select Low, Normal, or High, which specify share values respectively in a 1:2:4 ratio. Select Custom to give each virtual machine a specific number of shares, which expresses a proportional weight.

Guaranteed memory allocation for this resource pool.

Upper limit for this resource pool’s memory allocation. Select Unlimited to specify no upper limit.

5 Click OK.

Changing Resource Allocation Settings—Example

The following example illustrates how you can change resource allocation settings to improve virtual machine performance.

Assume that on an ESXi host, you have created two new virtual machines—one each for your QA (VM-QA) and Marketing (VM-Marketing) departments.

Figure 2‑1. Single Host with Two Virtual Machines

In the following example, assume that VM-QA is memory intensive and accordingly you want to change the resource allocation settings for the two virtual machines to:

Specify that, when system memory is overcommitted, VM-QA can use twice as much CPU and memory

resources as the Marketing virtual machine. Set the CPU shares and memory shares for VM-QA to High and for VM-Marketing set them to Normal.

Ensure that the Marketing virtual machine has a certain amount of guaranteed CPU resources. You can

do so using a reservation setting.

Procedure

1 Browse to the virtual machines in the vSphere Web Client navigator.

2 Right-click VM-QA, the virtual machine for which you want to change shares, and select Edit Settings.

3 Under Virtual Hardware, expand CPU and select High from the Shares drop-down menu.

4 Under Virtual Hardware, expand Memory and select High from the Shares drop-down menu.

5 Click OK.

6 Right-click the marketing virtual machine (VM-Marketing) and select Edit Settings.

7 Under Virtual Hardware, expand CPU and change the Reservation value to the desired number.

8 Click OK.

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If you select the cluster’s Resource Reservation tab and click CPU, you should see that shares for VM-QA are twice that of the other virtual machine. Also, because the virtual machines have not been powered on, the Reservation Used fields have not changed.

Admission Control

When you power on a virtual machine, the system checks the amount of CPU and memory resources that have not yet been reserved. Based on the available unreserved resources, the system determines whether it can guarantee the reservation for which the virtual machine is configured (if any). This process is called admission control.

If enough unreserved CPU and memory are available, or if there is no reservation, the virtual machine is powered on. Otherwise, an Insufficient Resources warning appears.

NOTE In addition to the user-specified memory reservation, for each virtual machine there is also an amount of overhead memory. This extra memory commitment is included in the admission control calculation.

When the vSphere DPM feature is enabled, hosts might be placed in standby mode (that is, powered off) to reduce power consumption. The unreserved resources provided by these hosts are considered available for admission control. If a virtual machine cannot be powered on without these resources, a recommendation to power on sufficient standby hosts is made.

Chapter 2 Configuring Resource Allocation Settings

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CPU Virtualization Basics 3

CPU virtualization emphasizes performance and runs directly on the processor whenever possible. The underlying physical resources are used whenever possible and the virtualization layer runs instructions only as needed to make virtual machines operate as if they were running directly on a physical machine.

CPU virtualization is not the same thing as emulation. ESXi does not use emulation to run virtual CPUs. With emulation, all operations are run in software by an emulator. A software emulator allows programs to run on a computer system other than the one for which they were originally written. The emulator does this by emulating, or reproducing, the original computer’s behavior by accepting the same data or inputs and achieving the same results. Emulation provides portability and runs software designed for one platform across several platforms.

When CPU resources are overcommitted, the ESXi host time-slices the physical processors across all virtual machines so each virtual machine runs as if it has its specified number of virtual processors. When an ESXi host runs multiple virtual machines, it allocates to each virtual machine a share of the physical resources. With the default resource allocation settings, all virtual machines associated with the same host receive an equal share of CPU per virtual CPU. This means that a single-processor virtual machines is assigned only half of the resources of a dual-processor virtual machine.

This chapter includes the following topics:

“Software-Based CPU Virtualization,” on page 19

“Hardware-Assisted CPU Virtualization,” on page 20

“Virtualization and Processor-Specific Behavior,” on page 20

“Performance Implications of CPU Virtualization,” on page 20

Software-Based CPU Virtualization

With software-based CPU virtualization, the guest application code runs directly on the processor, while the guest privileged code is translated and the translated code executes on the processor.

The translated code is slightly larger and usually executes more slowly than the native version. As a result, guest programs, which have a small privileged code component, run with speeds very close to native. Programs with a significant privileged code component, such as system calls, traps, or page table updates can run slower in the virtualized environment.

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Hardware-Assisted CPU Virtualization

Certain processors provide hardware assistance for CPU virtualization.

When using this assistance, the guest can use a separate mode of execution called guest mode. The guest code, whether application code or privileged code, runs in the guest mode. On certain events, the processor exits out of guest mode and enters root mode. The hypervisor executes in the root mode, determines the reason for the exit, takes any required actions, and restarts the guest in guest mode.

When you use hardware assistance for virtualization, there is no need to translate the code. As a result, system calls or trap-intensive workloads run very close to native speed. Some workloads, such as those involving updates to page tables, lead to a large number of exits from guest mode to root mode. Depending on the number of such exits and total time spent in exits, hardware-assisted CPU virtualization can speed up execution significantly.

Virtualization and Processor-Specific Behavior

Although VMware software virtualizes the CPU, the virtual machine detects the specific model of the processor on which it is running.

Processor models might differ in the CPU features they offer, and applications running in the virtual machine can make use of these features. Therefore, it is not possible to use vMotion® to migrate virtual machines between systems running on processors with different feature sets. You can avoid this restriction, in some cases, by using Enhanced vMotion Compatibility (EVC) with processors that support this feature. See the vCenter Server and Host Management documentation for more information.

Performance Implications of CPU Virtualization

CPU virtualization adds varying amounts of overhead depending on the workload and the type of virtualization used.

An application is CPU-bound if it spends most of its time executing instructions rather than waiting for external events such as user interaction, device input, or data retrieval. For such applications, the CPU virtualization overhead includes the additional instructions that must be executed. This overhead takes CPU processing time that the application itself can use. CPU virtualization overhead usually translates into a reduction in overall performance.

For applications that are not CPU-bound, CPU virtualization likely translates into an increase in CPU use. If spare CPU capacity is available to absorb the overhead, it can still deliver comparable performance in terms of overall throughput.

ESXi supports up to 128 virtual processors (CPUs) for each virtual machine.

NOTE Deploy single-threaded applications on uniprocessor virtual machines, instead of on SMP virtual machines that have multiple CPUs, for the best performance and resource use.

Single-threaded applications can take advantage only of a single CPU. Deploying such applications in dualprocessor virtual machines does not speed up the application. Instead, it causes the second virtual CPU to use physical resources that other virtual machines could otherwise use.

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Administering CPU Resources 4

You can configure virtual machines with one or more virtual processors, each with its own set of registers and control structures.

When a virtual machine is scheduled, its virtual processors are scheduled to run on physical processors. The VMkernel Resource Manager schedules the virtual CPUs on physical CPUs, thereby managing the virtual machine’s access to physical CPU resources. ESXi supports virtual machines with up to 128 virtual CPUs.

This chapter includes the following topics:

“View Processor Information,” on page 21

“Specifying CPU Configuration,” on page 21

“Multicore Processors,” on page 22

“Hyperthreading,” on page 22

“Using CPU Affinity,” on page 24

“Host Power Management Policies,” on page 25

View Processor Information

You can access information about current CPU configuration in the vSphere Web Client.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Select Processors to view the information about the number and type of physical processors and the

number of logical processors.

NOTE In hyperthreaded systems, each hardware thread is a logical processor. For example, a dual-core processor with hyperthreading enabled has two cores and four logical processors.

Specifying CPU Configuration

You can specify CPU configuration to improve resource management. However, if you do not customize CPU configuration, the ESXi host uses defaults that work well in most situations.

You can specify CPU configuration in the following ways:

Use the attributes and special features available through the vSphere Web Client. The

vSphere Web Client allows you to connect to the ESXi host or a vCenter Server system.

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Use advanced settings under certain circumstances.

Use the vSphere SDK for scripted CPU allocation.

Use hyperthreading.

Multicore Processors

Multicore processors provide many advantages for a host performing multitasking of virtual machines.

Intel and AMD have each developed processors which combine two or more processor cores into a single integrated circuit (often called a package or socket). VMware uses the term socket to describe a single package which can have one or more processor cores with one or more logical processors in each core.

A dual-core processor, for example, can provide almost double the performance of a single-core processor, by allowing two virtual CPUs to execute at the same time. Cores within the same processor are typically configured with a shared last-level cache used by all cores, potentially reducing the need to access slower main memory. A shared memory bus that connects a physical processor to main memory can limit performance of its logical processors if the virtual machines running on them are running memory-intensive workloads which compete for the same memory bus resources.

Each logical processor of each processor core can be used independently by the ESXi CPU scheduler to execute virtual machines, providing capabilities similar to SMP systems. For example, a two-way virtual machine can have its virtual processors running on logical processors that belong to the same core, or on logical processors on different physical cores.

The ESXi CPU scheduler can detect the processor topology and the relationships between processor cores and the logical processors on them. It uses this information to schedule virtual machines and optimize performance.

The ESXi CPU scheduler can interpret processor topology, including the relationship between sockets, cores, and logical processors. The scheduler uses topology information to optimize the placement of virtual CPUs onto different sockets to maximize overall cache utilization, and to improve cache affinity by minimizing virtual CPU migrations.

In some cases, such as when an SMP virtual machine exhibits significant data sharing between its virtual CPUs, this default behavior might be sub-optimal. For such workloads, it can be beneficial to schedule all of the virtual CPUs on the same socket, with a shared last-level cache, even when the ESXi host is undercommitted. In such scenarios, you can override the default behavior of spreading virtual CPUs across packages by including the following configuration option in the virtual machine's .vmx configuration file:

sched.cpu.vsmpConsolidate="TRUE".

Hyperthreading

Hyperthreading technology allows a single physical processor core to behave like two logical processors. The processor can run two independent applications at the same time. To avoid confusion between logical and physical processors, Intel refers to a physical processor as a socket, and the discussion in this chapter uses that terminology as well.

Intel Corporation developed hyperthreading technology to enhance the performance of its Pentium IV and Xeon processor lines. Hyperthreading technology allows a single processor core to execute two independent threads simultaneously.

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Chapter 4 Administering CPU Resources

While hyperthreading does not double the performance of a system, it can increase performance by better utilizing idle resources leading to greater throughput for certain important workload types. An application running on one logical processor of a busy core can expect slightly more than half of the throughput that it obtains while running alone on a non-hyperthreaded processor. Hyperthreading performance improvements are highly application-dependent, and some applications might see performance degradation with hyperthreading because many processor resources (such as the cache) are shared between logical processors.

NOTE On processors with Intel Hyper-Threading technology, each core can have two logical processors which share most of the core's resources, such as memory caches and functional units. Such logical processors are usually called threads.

Many processors do not support hyperthreading and as a result have only one thread per core. For such processors, the number of cores also matches the number of logical processors. The following processors support hyperthreading and have two threads per core.

Processors based on the Intel Xeon 5500 processor microarchitecture.

Intel Pentium 4 (HT-enabled)

Intel Pentium EE 840 (HT-enabled)

Hyperthreading and ESXi Hosts

A host that is enabled for hyperthreading should behave similarly to a host without hyperthreading. You might need to consider certain factors if you enable hyperthreading, however.

ESXi hosts manage processor time intelligently to guarantee that load is spread smoothly across processor cores in the system. Logical processors on the same core have consecutive CPU numbers, so that CPUs 0 and 1 are on the first core together, CPUs 2 and 3 are on the second core, and so on. Virtual machines are preferentially scheduled on two different cores rather than on two logical processors on the same core.

If there is no work for a logical processor, it is put into a halted state, which frees its execution resources and allows the virtual machine running on the other logical processor on the same core to use the full execution resources of the core. The VMware scheduler properly accounts for this halt time, and charges a virtual machine running with the full resources of a core more than a virtual machine running on a half core. This approach to processor management ensures that the server does not violate any of the standard ESXi resource allocation rules.

Consider your resource management needs before you enable CPU affinity on hosts using hyperthreading. For example, if you bind a high priority virtual machine to CPU 0 and another high priority virtual machine to CPU 1, the two virtual machines have to share the same physical core. In this case, it can be impossible to meet the resource demands of these virtual machines. Ensure that any custom affinity settings make sense for a hyperthreaded system.

Enable Hyperthreading

To enable hyperthreading, you must first enable it in your system's BIOS settings and then turn it on in the vSphere Web Client. Hyperthreading is enabled by default.

Consult your system documentation to determine whether your CPU supports hyperthreading.

Procedure

1 Ensure that your system supports hyperthreading technology.

2 Enable hyperthreading in the system BIOS.

Some manufacturers label this option Logical Processor, while others call it Enable Hyperthreading.

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3 Ensure that hyperthreading is enabled for the ESXi host.

a Browse to the host in the vSphere Web Client navigator.

b Click the Manage tab and click Settings.

c Under System, click Advanced System Settings and select VMkernel.Boot.hyperthreading.

Hyperthreading is enabled if the value is true.

4 Under Hardware, click Processors to view the number of Logical processors.

Hyperthreading is enabled.

Using CPU Affinity

By specifying a CPU affinity setting for each virtual machine, you can restrict the assignment of virtual machines to a subset of the available processors in multiprocessor systems. By using this feature, you can assign each virtual machine to processors in the specified affinity set.

CPU affinity specifies virtual machine-to-processor placement constraints and is different from the relationship created by a VM-VM or VM-Host affinity rule, which specifies virtual machine-to-virtual machine host placement constraints.

In this context, the term CPU refers to a logical processor on a hyperthreaded system and refers to a core on a non-hyperthreaded system.

The CPU affinity setting for a virtual machine applies to all of the virtual CPUs associated with the virtual machine and to all other threads (also known as worlds) associated with the virtual machine. Such virtual machine threads perform processing required for emulating mouse, keyboard, screen, CD-ROM, and miscellaneous legacy devices.

In some cases, such as display-intensive workloads, significant communication might occur between the virtual CPUs and these other virtual machine threads. Performance might degrade if the virtual machine's affinity setting prevents these additional threads from being scheduled concurrently with the virtual machine's virtual CPUs. Examples of this include a uniprocessor virtual machine with affinity to a single CPU or a two-way SMP virtual machine with affinity to only two CPUs.

For the best performance, when you use manual affinity settings, VMware recommends that you include at least one additional physical CPU in the affinity setting to allow at least one of the virtual machine's threads to be scheduled at the same time as its virtual CPUs. Examples of this include a uniprocessor virtual machine with affinity to at least two CPUs or a two-way SMP virtual machine with affinity to at least three CPUs.

Assign a Virtual Machine to a Specific Processor

Using CPU affinity, you can assign a virtual machine to a specific processor. This allows you to restrict the assignment of virtual machines to a specific available processor in multiprocessor systems.

Procedure

1 Find the virtual machine in the vSphere Web Client inventory.

a To find a virtual machine, select a data center, folder, cluster, resource pool, or host.

b Click the Related Objects tab and click Virtual Machines.

2 Right-click the virtual machine and click Edit Settings.

3 Under Virtual Hardware, expand CPU.

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4 Under Scheduling Affinity, select physical processor affinity for the virtual machine.

Use '-' for ranges and ',' to separate values.

For example, "0, 2, 4-7" would indicate processors 0, 2, 4, 5, 6 and 7.

5 Select the processors where you want the virtual machine to run and click OK.

Potential Issues with CPU Affinity

Before you use CPU affinity, you might need to consider certain issues.

Potential issues with CPU affinity include:

For multiprocessor systems, ESXi systems perform automatic load balancing. Avoid manual

specification of virtual machine affinity to improve the scheduler’s ability to balance load across processors.

Affinity can interfere with the ESXi host’s ability to meet the reservation and shares specified for a

virtual machine.

Because CPU admission control does not consider affinity, a virtual machine with manual affinity

settings might not always receive its full reservation.

Virtual machines that do not have manual affinity settings are not adversely affected by virtual machines with manual affinity settings.

Chapter 4 Administering CPU Resources

When you move a virtual machine from one host to another, affinity might no longer apply because the

new host might have a different number of processors.

The NUMA scheduler might not be able to manage a virtual machine that is already assigned to certain

processors using affinity.

Affinity can affect the host's ability to schedule virtual machines on multicore or hyperthreaded

processors to take full advantage of resources shared on such processors.

Host Power Management Policies

ESXi can take advantage of several power management features that the host hardware provides to adjust the trade-off between performance and power use. You can control how ESXi uses these features by selecting a power management policy.

In general, selecting a high-performance policy provides more absolute performance, but at lower efficiency (performance per watt). Lower-power policies provide less absolute performance, but at higher efficiency.

ESXi provides five power management policies. If the host does not support power management, or if the BIOS settings specify that the host operating system is not allowed to manage power, only the Not Supported policy is available.

You select a policy for a host using the vSphere Web Client. If you do not select a policy, ESXi uses Balanced by default.

Table 4‑1. CPU Power Management Policies

Power Management Policy Description

Not supported The host does not support any power management features

High Performance The VMkernel detects certain power management features,

Balanced (Default) The VMkernel uses the available power management

or power management is not enabled in the BIOS.

but will not use them unless the BIOS requests them for power capping or thermal events.

features conservatively to reduce host energy consumption with minimal compromise to performance.

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vSphere Resource Management

Table 4‑1. CPU Power Management Policies (Continued)

Power Management Policy Description

Low Power The VMkernel aggressively uses available power

Custom The VMkernel bases its power management policy on the

When a CPU runs at lower frequency, it can also run at lower voltage, which saves power. This type of power management is typically called Dynamic Voltage and Frequency Scaling (DVFS). ESXi attempts to adjust CPU frequencies so that virtual machine performance is not affected.

When a CPU is idle, ESXi can take advantage of deep halt states (known as C-states). The deeper the C-state, the less power the CPU uses, but the longer it takes for the CPU to resume running. When a CPU becomes idle, ESXi applies an algorithm to predict how long it will be in an idle state and chooses an appropriate Cstate to enter. In power management policies that do not use deep C-states, ESXi uses only the shallowest halt state (C1) for idle CPUs.

Select a CPU Power Management Policy

management features to reduce host energy consumption at the risk of lower performance.

values of several advanced configuration parameters. You can set these parameters in the vSphere Web Client Advanced Settings dialog box.

You set the CPU power management policy for a host using the vSphere Web Client.

Prerequisites

Verify that the BIOS settings on the host system allow the operating system to control power management (for example, OS Controlled).

NOTE Some systems have Processor Clocking Control (PCC) technology, which allows ESXi to manage power on the host system even if the host BIOS settings do not specify OS Controlled mode. With this technology, ESXi does not manage P-states directly. Instead, the host cooperates with the BIOS to determine the processor clock rate. HP systems that support this technology have a BIOS setting called Cooperative Power Management that is enabled by default.

If the host hardware does not allow the operating system to manage power, only the Not Supported policy is available. (On some systems, only the High Performance policy is available.)

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Hardware, select Power Management and click the Edit button.

4 Select a power management policy for the host and click OK.

The policy selection is saved in the host configuration and can be used again at boot time. You can change it at any time, and it does not require a server reboot.

Configure Custom Policy Parameters for Host Power Management

When you use the Custom policy for host power management, ESXi bases its power management policy on the values of several advanced configuration parameters.

Prerequisites

Select Custom for the power management policy, as described in “Select a CPU Power Management

Policy,” on page 26.

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Chapter 4 Administering CPU Resources

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under System, select Advanced System Settings.

4 In the right pane, you can edit the power management parameters that affect the Custom policy.

Power management parameters that affect the Custom policy have descriptions that begin with In Custom policy. All other power parameters affect all power management policies.

5 Select the parameter and click the Edit button.

NOTE The default values of power management parameters match the Balanced policy.

Parameter Description

Power.UsePStates

Power.MaxCpuLoad

Power.MinFreqPct

Power.UseStallCtr

Power.TimerHz

Power.UseCStates

Power.CStateMaxLatency

Power.CStateResidencyCoef

Power.CStatePredictionCoef

Power.PerfBias

Use ACPI P-states to save power when the processor is busy.

Use P-states to save power on a CPU only when the CPU is busy for less than the given percentage of real time.

Do not use any P-states slower than the given percentage of full CPU speed.

Use a deeper P-state when the processor is frequently stalled waiting for events such as cache misses.

Controls how many times per second ESXi reevaluates which P-state each CPU should be in.

Use deep ACPI C-states (C2 or below) when the processor is idle.

Do not use C-states whose latency is greater than this value.

When a CPU becomes idle, choose the deepest C-state whose latency multiplied by this value is less than the host's prediction of how long the CPU will remain idle. Larger values make ESXi more conservative about using deep C-states, while smaller values are more aggressive.

A parameter in the ESXi algorithm for predicting how long a CPU that becomes idle will remain idle. Changing this value is not recommended.

Performance Energy Bias Hint (Intel-only). Sets an MSR on Intel processors to an Intel-recommended value. Intel recommends 0 for high performance, 6 for balanced, and 15 for low power. Other values are undefined.

6 Click OK.

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Memory Virtualization Basics 5

Before you manage memory resources, you should understand how they are being virtualized and used by ESXi.

The VMkernel manages all physical RAM on the host. The VMkernel dedicates part of this managed physical RAM for its own use. The rest is available for use by virtual machines.

The virtual and physical memory space is divided into blocks called pages. When physical memory is full, the data for virtual pages that are not present in physical memory are stored on disk. Depending on processor architecture, pages are typically 4 KB or 2 MB. See “Advanced Memory Attributes,” on page 116.

This chapter includes the following topics:

“Virtual Machine Memory,” on page 29

“Memory Overcommitment,” on page 30

“Memory Sharing,” on page 30

“Types of Memory Virtualization,” on page 31

Virtual Machine Memory

Each virtual machine consumes memory based on its configured size, plus additional overhead memory for virtualization.

The configured size is the amount of memory that is presented to the guest operating system. This is different from the amount of physical RAM that is allocated to the virtual machine. The latter depends on the resource settings (shares, reservation, limit) and the level of memory pressure on the host.

For example, consider a virtual machine with a configured size of 1GB. When the guest operating system boots, it detects that it is running on a dedicated machine with 1GB of physical memory. In some cases, the virtual machine might be allocated the full 1GB. In other cases, it might receive a smaller allocation. Regardless of the actual allocation, the guest operating system continues to behave as though it is running on a dedicated machine with 1GB of physical memory.

Reservation

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Specify the relative priority for a virtual machine if more than the reservation is available.

Is a guaranteed lower bound on the amount of physical RAM that the host reserves for the virtual machine, even when memory is overcommitted. Set the reservation to a level that ensures the virtual machine has sufficient memory to run efficiently, without excessive paging.

vSphere Resource Management

After a virtual machine consumes all of the memory within its reservation, it is allowed to retain that amount of memory and this memory is not reclaimed, even if the virtual machine becomes idle. Some guest operating systems (for example, Linux) might not access all of the configured memory immediately after booting. Until the virtual machines consumes all of the memory within its reservation, VMkernel can allocate any unused portion of its reservation to other virtual machines. However, after the guest’s workload increases and the virtual machine consumes its full reservation, it is allowed to keep this memory.

Limit

Is an upper bound on the amount of physical RAM that the host can allocate to the virtual machine. The virtual machine’s memory allocation is also implicitly limited by its configured size.

Memory Overcommitment

For each running virtual machine, the system reserves physical RAM for the virtual machine’s reservation (if any) and for its virtualization overhead.

The total configured memory sizes of all virtual machines may exceed the amount of available physical memory on the host. However, it doesn't necessarily mean memory is overcommitted. Memory is overcommitted when the combined working memory footprint of all virtual machines exceed that of the host memory sizes.

Because of the memory management techniques the ESXi host uses, your virtual machines can use more virtual RAM than there is physical RAM available on the host. For example, you can have a host with 2GB memory and run four virtual machines with 1GB memory each. In that case, the memory is overcommitted. For instance, if all four virtual machines are idle, the combined consumed memory may be well below 2GB. However, if all 4GB virtual machines are actively consuming memory, then their memory footprint may exceed 2GB and the ESXi host will become overcommitted.

Overcommitment makes sense because, typically, some virtual machines are lightly loaded while others are more heavily loaded, and relative activity levels vary over time.

To improve memory utilization, the ESXi host transfers memory from idle virtual machines to virtual machines that need more memory. Use the Reservation or Shares parameter to preferentially allocate memory to important virtual machines. This memory remains available to other virtual machines if it is not in use. ESXi implements various mechanisms such as ballooning, memory sharing, memory compression and swapping to provide reasonable performance even if the host is not heavily memory overcommitted.

An ESXi host can run out of memory if virtual machines consume all reservable memory in a memory overcommitted environment. Although the powered on virtual machines are not affected, a new virtual machine might fail to power on due to lack of memory.

NOTE All virtual machine memory overhead is also considered reserved.

In addition, memory compression is enabled by default on ESXi hosts to improve virtual machine performance when memory is overcommitted as described in “Memory Compression,” on page 43.

Memory Sharing

Memory sharing is a proprietary ESXi technique that can help achieve greater memory density on a host.

Memory sharing relies on the observation that several virtual machines might be running instances of the same guest operating system, have the same applications or components loaded, or contain common data. In such cases, a host uses a proprietary Transparent Page Sharing (TPS) technique to eliminate redundant copies of memory pages. With memory sharing, a workload running in virtual machines often consumes

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less memory than it would when running on physical machines. As a result, higher levels of

virtual machine

guest virtual memory

guest physical memory

machine memory

a b

a b b c

c b

b c

virtual machine

overcommitment can be supported efficiently. The amount of memory saved by memory sharing depends on whether the workload consists of nearly identical machines which might free up more memory, while a more diverse workload might result in a signifigantly lower percentage of memory savings.

NOTE Due to security concerns, inter-virtual machine transparent page sharing is disabled by default and page sharing is being restricted to intra-virtual machine memory sharing. This means page sharing does not occur across virtual machines and only occurs inside of a virtual machine. See “Sharing Memory Across

Virtual Machines,” on page 42 for more information.

Types of Memory Virtualization

There are two types of memory virtualization: Software-based and hardware-assisted memory virtualization.

Because of the extra level of memory mapping introduced by virtualization, ESXi can effectively manage memory across all virtual machines. Some of the physical memory of a virtual machine might be mapped to shared pages or to pages that are unmapped, or swapped out.

A host performs virtual memory management without the knowledge of the guest operating system and without interfering with the guest operating system’s own memory management subsystem.

The VMM for each virtual machine maintains a mapping from the guest operating system's physical memory pages to the physical memory pages on the underlying machine. (VMware refers to the underlying host physical pages as “machine” pages and the guest operating system’s physical pages as “physical” pages.)

Chapter 5 Memory Virtualization Basics

Each virtual machine sees a contiguous, zero-based, addressable physical memory space. The underlying machine memory on the server used by each virtual machine is not necessarily contiguous.

For both software-based and hardware-assisted memory virtualization, the guest virtual to guest physical addresses are managed by the guest operating system. The hypervisor is only responsible for translating the guest physical addresses to machine addresses. Software-based memory virtualization combines the guest's virtual to machine addresses in software and saves them in the shadow page tables managed by the hypervisor. Hardware-assisted memory virtualization utilizes the hardware facility to generate the combined mappings with the guest's page tables and the nested page tables maintained by the hypervisor.

The diagram illustrates the ESXi implementation of memory virtualization.

Figure 5‑1. ESXi Memory Mapping

The boxes represent pages, and the arrows show the different memory mappings.

The arrows from guest virtual memory to guest physical memory show the mapping maintained by the

page tables in the guest operating system. (The mapping from virtual memory to linear memory for x86-architecture processors is not shown.)

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The arrows from guest physical memory to machine memory show the mapping maintained by the

VMM.

vSphere Resource Management

The dashed arrows show the mapping from guest virtual memory to machine memory in the shadow

page tables also maintained by the VMM. The underlying processor running the virtual machine uses the shadow page table mappings.

Software-Based Memory Virtualization

ESXi virtualizes guest physical memory by adding an extra level of address translation.

The VMM maintains the combined virtual-to-machine page mappings in the shadow page tables. The

shadow page tables are kept up to date with the guest operating system's virtual-to-physical mappings and physical-to-machine mappings maintained by the VMM.

The VMM intercepts virtual machine instructions that manipulate guest operating system memory

management structures so that the actual memory management unit (MMU) on the processor is not updated directly by the virtual machine.

The shadow page tables are used directly by the processor's paging hardware.

There is non-trivial computation overhead for maintaining the coherency of the shadow page tables.

The overhead is more pronounced when the number of virtual CPUs increases.

This approach to address translation allows normal memory accesses in the virtual machine to execute without adding address translation overhead, after the shadow page tables are set up. Because the translation look-aside buffer (TLB) on the processor caches direct virtual-to-machine mappings read from the shadow page tables, no additional overhead is added by the VMM to access the memory. Note that software MMU has a higher overhead memory requirement than hardware MMU. Hence, in order to support software MMU, the maximum overhead supported for virtual machines in the VMkernel needs to be increased. In some cases, software memory virtualization may have some performance benefit over hardware-assisted approach if the workload induces a huge amount of TLB misses.

Performance Considerations

The use of two sets of page tables has these performance implications.

No overhead is incurred for regular guest memory accesses.

Additional time is required to map memory within a virtual machine, which happens when:

The virtual machine operating system is setting up or updating virtual address to physical address

mappings.

The virtual machine operating system is switching from one address space to another (context

switch).

Like CPU virtualization, memory virtualization overhead depends on workload.

Hardware-Assisted Memory Virtualization

Some CPUs, such as AMD SVM-V and the Intel Xeon 5500 series, provide hardware support for memory virtualization by using two layers of page tables.

The first layer of page tables stores guest virtual-to-physical translations, while the second layer of page tables stores guest physical-to-machine translation. The TLB (translation look-aside buffer) is a cache of translations maintained by the processor's memory management unit (MMU) hardware. A TLB miss is a miss in this cache and the hardware needs to go to memory (possibly many times) to find the required translation. For a TLB miss to a certain guest virtual address, the hardware looks at both page tables to translate guest virtual address to machine address. The first layer of page tables is maintained by the guest operating system. The VMM only maintains the second layer of page tables.

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Chapter 5 Memory Virtualization Basics

Performance Considerations

When you use hardware assistance, you eliminate the overhead for software memory virtualization. In particular, hardware assistance eliminates the overhead required to keep shadow page tables in synchronization with guest page tables. However, the TLB miss latency when using hardware assistance is significantly higher. By default the hypervisor uses large pages in hardware assisted modes to reduce the cost of TLB misses. As a result, whether or not a workload benefits by using hardware assistance primarily depends on the overhead the memory virtualization causes when using software memory virtualization. If a workload involves a small amount of page table activity (such as process creation, mapping the memory, or context switches), software virtualization does not cause significant overhead. Conversely, workloads with a large amount of page table activity are likely to benefit from hardware assistance.

The performance of hardware MMU has improved since it was first introduced with extensive caching implemented in hardware. Using software memory virtualization techniques, the frequency of context switches in a typical guest may happen from 100 to 1000 times per second. Each context switch will trap the VMM in software MMU. Hardware MMU approaches avoid this issue.

By default the hypervisor uses large pages in hardware assisted modes to reduce the cost of TLB misses. The best performance is achieved by using large pages in both guest virtual to guest physical and guest physical to machine address translations.

The option LPage.LPageAlwaysTryForNPT can change the policy for using large pages in guest physical to machine address translations. For more information, see “Advanced Memory Attributes,” on page 116.

NOTE Binary translation only works with software-based memory virtualization.

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Administering Memory Resources 6

Using the vSphere Web Client you can view information about and make changes to memory allocation settings. To administer your memory resources effectively, you must also be familiar with memory overhead, idle memory tax, and how ESXi hosts reclaim memory.

When administering memory resources, you can specify memory allocation. If you do not customize memory allocation, the ESXi host uses defaults that work well in most situations.

You can specify memory allocation in several ways.

Use the attributes and special features available through the vSphere Web Client. The

vSphere Web Client allows you to connect to the ESXi host or vCenter Server system.

Use advanced settings.

Use the vSphere SDK for scripted memory allocation.

This chapter includes the following topics:

“Understanding Memory Overhead,” on page 35

“How ESXi Hosts Allocate Memory,” on page 36

“Memory Reclamation,” on page 37

“Using Swap Files,” on page 38

“Sharing Memory Across Virtual Machines,” on page 42

“Memory Compression,” on page 43

“Measuring and Differentiating Types of Memory Usage,” on page 44

“Memory Reliability,” on page 45

“About System Swap,” on page 45

Understanding Memory Overhead

Virtualization of memory resources has some associated overhead.

ESXi virtual machines can incur two kinds of memory overhead.

The additional time to access memory within a virtual machine.

The extra space needed by the ESXi host for its own code and data structures, beyond the memory

allocated to each virtual machine.

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vSphere Resource Management

ESXi memory virtualization adds little time overhead to memory accesses. Because the processor's paging hardware uses page tables (shadow page tables for software-based approach or two level page tables for hardware-assisted approach) directly, most memory accesses in the virtual machine can execute without address translation overhead.

The memory space overhead has two components.

A fixed, system-wide overhead for the VMkernel.

Additional overhead for each virtual machine.

Overhead memory includes space reserved for the virtual machine frame buffer and various virtualization data structures, such as shadow page tables. Overhead memory depends on the number of virtual CPUs and the configured memory for the guest operating system.

Overhead Memory on Virtual Machines

Virtual machines require a certain amount of available overhead memory to power on. You should be aware of the amount of this overhead.

The amount of overhead memory needed for a virtual machine depends on a large number of factors, including the number of vCPUs and memory size, the number and types of devices, the execution mode that the monitor is using and the hardware version of the virtual machine. The version of vSphere you are using can also effect the amount of memory needed. VMX automatically calculates the amount of overhead memory needed for a virtual machine.

In order to find out how much overhead memory is needed for your specific configuration, first power on the virtual machine in question. Look in the vmware.log file. When the virtual machine powers on, the amount of overhead memory it needs is printed to the log. Search within the log for VMMEM to see the initial and precise amount of overhead memory reserved for the virtual machine.

How ESXi Hosts Allocate Memory

A host allocates the memory specified by the Limit parameter to each virtual machine, unless memory is overcommitted. ESXi never allocates more memory to a virtual machine than its specified physical memory size.

For example, a 1GB virtual machine might have the default limit (unlimited) or a user-specified limit (for example 2GB). In both cases, the ESXi host never allocates more than 1GB, the physical memory size that was specified for it.

When memory is overcommitted, each virtual machine is allocated an amount of memory somewhere between what is specified by Reservation and what is specified by Limit. The amount of memory granted to a virtual machine above its reservation usually varies with the current memory load.

A host determines allocations for each virtual machine based on the number of shares allocated to it and an estimate of its recent working set size.

Shares — ESXi hosts use a modified proportional-share memory allocation policy. Memory shares

entitle a virtual machine to a fraction of available physical memory.

Working set size — ESXi hosts estimate the working set for a virtual machine by monitoring memory

activity over successive periods of virtual machine execution time. Estimates are smoothed over several time periods using techniques that respond rapidly to increases in working set size and more slowly to decreases in working set size.

This approach ensures that a virtual machine from which idle memory is reclaimed can ramp up quickly to its full share-based allocation when it starts using its memory more actively.

Memory activity is monitored to estimate the working set sizes for a default period of 60 seconds. To modify this default , adjust the Mem.SamplePeriod advanced setting. See “Set Advanced Host

Attributes,” on page 115.

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Chapter 6 Administering Memory Resources

Memory Tax for Idle Virtual Machines

If a virtual machine is not actively using all of its currently allocated memory, ESXi charges more for idle memory than for memory that is in use. This is done to help prevent virtual machines from hoarding idle memory.

The idle memory tax is applied in a progressive fashion. The effective tax rate increases as the ratio of idle memory to active memory for the virtual machine rises. (In earlier versions of ESXi that did not support hierarchical resource pools, all idle memory for a virtual machine was taxed equally.)

You can modify the idle memory tax rate with the Mem.IdleTax option. Use this option, together with the

Mem.SamplePeriod advanced attribute, to control how the system determines target memory allocations for

virtual machines. See “Set Advanced Host Attributes,” on page 115.

NOTE In most cases, changes to Mem.IdleTax are not necessary nor appropriate.

VMX Swap Files

Virtual machine executable (VMX) swap files allow the host to greatly reduce the amount of overhead memory reserved for the VMX process.

NOTE VMX swap files are not related to the swap to host swap cache feature or to regular host-level swap files.

ESXi reserves memory per virtual machine for a variety of purposes. Memory for the needs of certain components, such as the virtual machine monitor (VMM) and virtual devices, is fully reserved when a virtual machine is powered on. However, some of the overhead memory that is reserved for the VMX process can be swapped. The VMX swap feature reduces the VMX memory reservation significantly (for example, from about 50MB or more per virtual machine to about 10MB per virtual machine). This allows the remaining memory to be swapped out when host memory is overcommitted, reducing overhead memory reservation for each virtual machine.

The host creates VMX swap files automatically, provided there is sufficient free disk space at the time a virtual machine is powered on.

Memory Reclamation

ESXi hosts can reclaim memory from virtual machines.

A host allocates the amount of memory specified by a reservation directly to a virtual machine. Anything beyond the reservation is allocated using the host’s physical resources or, when physical resources are not available, handled using special techniques such as ballooning or swapping. Hosts can use two techniques for dynamically expanding or contracting the amount of memory allocated to virtual machines.

ESXi systems use a memory balloon driver (vmmemctl), loaded into the guest operating system running

in a virtual machine. See “Memory Balloon Driver,” on page 38.

ESXi system swaps out a page from a virtual machine to a server swap file without any involvement by

the guest operating system. Each virtual machine has its own swap file.

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memory

swap space

vSphere Resource Management

Memory Balloon Driver

The memory balloon driver (vmmemctl) collaborates with the server to reclaim pages that are considered least valuable by the guest operating system.

The driver uses a proprietary ballooning technique that provides predictable performance that closely matches the behavior of a native system under similar memory constraints. This technique increases or decreases memory pressure on the guest operating system, causing the guest to use its own native memory management algorithms. When memory is tight, the guest operating system determines which pages to reclaim and, if necessary, swaps them to its own virtual disk.

Figure 6‑1. Memory Ballooning in the Guest Operating System

NOTE You must configure the guest operating system with sufficient swap space. Some guest operating systems have additional limitations.

If necessary, you can limit the amount of memory vmmemctl reclaims by setting the sched.mem.maxmemctl parameter for a specific virtual machine. This option specifies the maximum amount of memory that can be reclaimed from a virtual machine in megabytes (MB). See “Set Advanced Virtual Machine Attributes,” on page 118.

Using Swap Files

You can specify the location of your guest swap file, reserve swap space when memory is overcommitted,

38 VMware, Inc.

and delete a swap file.

ESXi hosts use swapping to forcibly reclaim memory from a virtual machine when the vmmemctl driver is not available or is not responsive.

It was never installed.

It is explicitly disabled.

It is not running (for example, while the guest operating system is booting).

It is temporarily unable to reclaim memory quickly enough to satisfy current system demands.

Chapter 6 Administering Memory Resources

It is functioning properly, but maximum balloon size is reached.

Standard demand-paging techniques swap pages back in when the virtual machine needs them.

Swap File Location

By default, the swap file is created in the same location as the virtual machine's configuration file, which could either be on a VMFS datastore, a vSAN datastore or a VVol datastore. On a vSAN datastore or a VVol datastore, the swap file is created as a separate vSANor VVol object.

A swap file is created by the ESXi host when a virtual machine is powered on. If this file cannot be created, the virtual machine cannot power on. Instead of accepting the default, you can also:

Use per-virtual machine configuration options to change the datastore to another shared storage

location.

Use host-local swap, which allows you to specify a datastore stored locally on the host. This allows you

to swap at a per-host level, saving space on the SAN. However, it can lead to a slight degradation in performance for vSphere vMotion because pages swapped to a local swap file on the source host must be transferred across the network to the destination host. Please note that currently vSAN and VVol datastores cannot be specified for host-local swap.

Enable Host-Local Swap for a DRS Cluster

Host-local swap allows you to specify a datastore stored locally on the host as the swap file location. You can enable host-local swap for a DRS cluster.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Configuration, click General to view the swap file location and click Edit to change it.

4 Select the Datastore specified by host option and click OK.

5 Browse to one of the hosts in the cluster in the vSphere Web Client navigator.

6 Click the Manage tab and click Settings.

7 Under Virtual Machines, select Virtual Machine Swapfile Location.

8 Click Edit and select the local datastore to use and click OK.

9 Repeat Step 5 through Step 8 for each host in the cluster.

Host-local swap is now enabled for the DRS cluster.

Enable Host-Local Swap for a Standalone Host

Host-local swap allows you to specify a datastore stored locally on the host as the swap file location. You can enable host-local swap for a standalone host.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Virtual Machines, select Virtual Machine Swapfile Location.

4 Click Edit and select Selected Datastore.

5 Select a local datastore from the list and click OK.

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vSphere Resource Management

Host-local swap is now enabled for the standalone host.

Swap Space and Memory Overcommitment

You must reserve swap space for any unreserved virtual machine memory (the difference between the reservation and the configured memory size) on per-virtual machine swap files.

This swap reservation is required to ensure that the ESXi host is able to preserve virtual machine memory under any circumstances. In practice, only a small fraction of the host-level swap space might be used.

If you are overcommitting memory with ESXi, to support the intra-guest swapping induced by ballooning, ensure that your guest operating systems also have sufficient swap space. This guest-level swap space must be greater than or equal to the difference between the virtual machine’s configured memory size and its Reservation.

CAUTION If memory is overcommitted, and the guest operating system is configured with insufficient swap space, the guest operating system in the virtual machine can fail.

To prevent virtual machine failure, increase the size of the swap space in your virtual machines.

Windows guest operating systems— Windows operating systems refer to their swap space as paging

files. Some Windows operating systems try to increase the size of paging files automatically, if there is sufficient free disk space.

See your Microsoft Windows documentation or search the Windows help files for “paging files.” Follow the instructions for changing the size of the virtual memory paging file.

Linux guest operating system — Linux operating systems refer to their swap space as swap files. For

information on increasing swap files, see the following Linux man pages:

mkswap — Sets up a Linux swap area.

swapon — Enables devices and files for paging and swapping.

Guest operating systems with a lot of memory and small virtual disks (for example, a virtual machine with 8GB RAM and a 2GB virtual disk) are more susceptible to having insufficient swap space.

NOTE Do not store swap files on thin-provisioned LUNs. Running a virtual machine with a swap file that is stored on a thin-provisioned LUN can cause swap file growth failure, which can lead to termination of the virtual machine.

When you create a large swap file (for example, larger than 100GB), the amount of time it takes for the virtual machine to power on can increase significantly. To avoid this, set a high reservation for large virtual machines.

You can also place swap files on less costly storage using host-local swap files.

Configure Virtual Machine Swapfile Properties for the Host

Configure a swapfile location for the host to determine the default location for virtual machine swapfiles in the vSphere Web Client.

By default, swapfiles for a virtual machine are located on a datastore in the folder that contains the other virtual machine files. However, you can configure your host to place virtual machine swapfiles on an alternative datastore.

You can use this option to place virtual machine swapfiles on lower-cost or higher-performance storage. You can also override this host-level setting for individual virtual machines.

40 VMware, Inc.

Chapter 6 Administering Memory Resources

Setting an alternative swapfile location might cause migrations with vMotion to complete more slowly. For best vMotion performance, store the virtual machine on a local datastore rather than in the same directory as the virtual machine swapfiles. If the virtual machine is stored on a local datastore, storing the swapfile with the other virtual machine files will not improve vMotion.

Prerequisites

Required privilege: Host machine.Configuration.Storage partition configuration

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Select the Manage tab and click Settings.

3 Under Virtual Machines, click Swap file location.

The selected swapfile location is displayed. If configuration of the swapfile location is not supported on the selected host, the tab indicates that the feature is not supported.

If the host is part of a cluster, and the cluster settings specify that swapfiles are to be stored in the same directory as the virtual machine, you cannot edit the swapfile location from the host Manage tab. To change the swapfile location for such a host, edit the cluster settings.

4 Click Edit.

5 Select where to store the swapfile.

Option Description

Virtual machine directory

Use a specific datastore

Stores the swapfile in the same directory as the virtual machine configuration file.

Stores the swapfile in the location you specify.

If the swapfile cannot be stored on the datastore that the host specifies, the swapfile is stored in the same folder as the virtual machine.

6 (Optional) If you select Use a specific datastore, select a datastore from the list.

7 Click OK.

The virtual machine swapfile is stored in the location you selected.

Configure a Virtual Machine Swapfile Location for a Cluster

By default, swapfiles for a virtual machine are located on a datastore in the folder that contains the other virtual machine files. However, you can instead configure the hosts in your cluster to place virtual machine swapfiles on an alternative datastore of your choice.

You can configure an alternative swapfile location to place virtual machine swapfiles on either lower-cost or higher-performance storage, depending on your needs.

Prerequisites

Before you configure a virtual machine swapfile location for a cluster, you must configure the virtual machine swapfile locations for the hosts in the cluster as described in “Configure Virtual Machine Swapfile

Properties for the Host,” on page 40.

Procedure

1 Browse to the cluster in the vSphere Web Client.

2 Click the Manage tab and click Settings.

3 Select Configuration > General.

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vSphere Resource Management

4 Next to Swap file location, click Edit.

5 Select where to store the swapfile.

Option Description

Virtual machine directory

Datastore specified by host

6 Click OK.

Delete Swap Files

If a host fails, and that host had running virtual machines that were using swap files, those swap files continue to exist and consume many gigabytes of disk space. You can delete the swap files to eliminate this problem.

Procedure

1 Restart the virtual machine that was on the host that failed.

Stores the swapfile in the same directory as the virtual machine configuration file.

Stores the swapfile in the location specified in the host configuration.

If the swapfile cannot be stored on the datastore that the host specifies, the swapfile is stored in the same folder as the virtual machine.

2 Stop the virtual machine.

The swap file for the virtual machine is deleted.

Sharing Memory Across Virtual Machines

Many ESXi workloads present opportunities for sharing memory across virtual machines (as well as within a single virtual machine).

ESXi memory sharing runs as a background activity that scans for sharing opportunities over time. The amount of memory saved varies over time. For a fairly constant workload, the amount generally increases slowly until all sharing opportunities are exploited.

To determine the effectiveness of memory sharing for a given workload, try running the workload, and use

resxtop or esxtop to observe the actual savings. Find the information in the PSHARE field of the interactive

mode in the Memory page.

Use the Mem.ShareScanTime and Mem.ShareScanGHz advanced settings to control the rate at which the system scans memory to identify opportunities for sharing memory.

You can also configure sharing for individual virtual machines by setting the sched.mem.pshare.enable option.

Due to security concerns, inter-virtual machine transparent page sharing is disabled by default and page sharing is being restricted to intra-virtual machine memory sharing. This means page sharing does not occur across virtual machines and only occurs inside of a virtual machine. The concept of salting has been introduced to help address concerns system administrators may have over the security implications of transparent page sharing. Salting can be used to allow more granular management of the virtual machines participating in transparent page sharing than was previously possible. With the new salting settings, virtual machines can share pages only if the salt value and contents of the pages are identical. A new host config option Mem.ShareForceSalting can be configured to enable or disable salting.

See Chapter 15, “Advanced Attributes,” on page 115 for information on how to set advanced options.

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Memory Compression

ESXi provides a memory compression cache to improve virtual machine performance when you use memory overcommitment. Memory compression is enabled by default. When a host's memory becomes overcommitted, ESXi compresses virtual pages and stores them in memory.

Because accessing compressed memory is faster than accessing memory that is swapped to disk, memory compression in ESXi allows you to overcommit memory without significantly hindering performance. When a virtual page needs to be swapped, ESXi first attempts to compress the page. Pages that can be compressed to 2 KB or smaller are stored in the virtual machine's compression cache, increasing the capacity of the host.

You can set the maximum size for the compression cache and disable memory compression using the Advanced Settings dialog box in the vSphere Web Client.

Enable or Disable the Memory Compression Cache

Memory compression is enabled by default. You can use Advanced System Settings in the vSphere Web Client to enable or disable memory compression for a host.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

Chapter 6 Administering Memory Resources

2 Click the Manage tab and click Settings.

3 Under System, select Advanced System Settings.

4 Locate Mem.MemZipEnable and click the Edit button.

5 Enter 1 to enable or enter 0 to disable the memory compression cache.

6 Click OK.

Set the Maximum Size of the Memory Compression Cache

You can set the maximum size of the memory compression cache for the host's virtual machines.

You set the size of the compression cache as a percentage of the memory size of the virtual machine. For example, if you enter 20 and a virtual machine's memory size is 1000 MB, ESXi can use up to 200MB of host memory to store the compressed pages of the virtual machine.

If you do not set the size of the compression cache, ESXi uses the default value of 10 percent.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under System, select Advanced System Settings.

4 Locate Mem.MemZipMaxPct and click the Edit button.

The value of this attribute determines the maximum size of the compression cache for the virtual machine.

5 Enter the maximum size for the compression cache.

The value is a percentage of the size of the virtual machine and must be between 5 and 100 percent.

6 Click OK.

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virtual machine

guest virtual memory

guest physical memory

machine memory

c c

virtual machine

vSphere Resource Management

Measuring and Differentiating Types of Memory Usage

The Performance tab of the vSphere Web Client displays a number of metrics that can be used to analyze memory usage.

Some of these memory metrics measure guest physical memory while other metrics measure machine memory. For instance, two types of memory usage that you can examine using performance metrics are guest physical memory and machine memory. You measure guest physical memory using the Memory Granted metric (for a virtual machine) or Memory Shared (for a host). To measure machine memory, however, use Memory Consumed (for a virtual machine) or Memory Shared Common (for a host). Understanding the conceptual difference between these types of memory usage is important for knowing what these metrics are measuring and how to interpret them.

The VMkernel maps guest physical memory to machine memory, but they are not always mapped one-toone. Multiple regions of guest physical memory might be mapped to the same region of machine memory (in the case of memory sharing) or specific regions of guest physical memory might not be mapped to machine memory (when the VMkernel swaps out or balloons guest physical memory). In these situations, calculations of guest physical memory usage and machine memory usage for an individual virtual machine or a host differ.

Consider the example in the following figure, which shows two virtual machines running on a host. Each block represents 4 KB of memory and each color/letter represents a different set of data on a block.

Figure 6‑2. Memory Usage Example

The performance metrics for the virtual machines can be determined as follows:

To determine Memory Granted (the amount of guest physical memory that is mapped to machine

memory) for virtual machine 1, count the number of blocks in virtual machine 1's guest physical memory that have arrows to machine memory and multiply by 4 KB. Since there are five blocks with arrows, Memory Granted would be 20 KB.

Memory Consumed is the amount of machine memory allocated to the virtual machine, accounting for

savings from shared memory. First, count the number of blocks in machine memory that have arrows from virtual machine 1's guest physical memory. There are three such blocks, but one block is shared with virtual machine 2. So count two full blocks plus half of the third and multiply by 4 KB for a total of 10 KB Memory Consumed.

The important difference between these two metrics is that Memory Granted counts the number of blocks with arrows at the guest physical memory level and Memory Consumed counts the number of blocks with arrows at the machine memory level. The number of blocks differs between the two levels due to memory sharing and so Memory Granted and Memory Consumed differ. This is not problematic and shows that memory is being saved through sharing or other reclamation techniques.

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A similar result is obtained when determining Memory Shared and Memory Shared Common for the host.

Memory Shared for the host is the sum of each virtual machine's Memory Shared. Calculate this by

looking at each virtual machine's guest physical memory and counting the number of blocks that have arrows to machine memory blocks that themselves have more than one arrow pointing at them. There are six such blocks in the example, so Memory Shared for the host is 24 KB.

Memory Shared Common is the amount of machine memory that is shared by virtual machines. To

determine this, look at the machine memory and count the number of blocks that have more than one arrow pointing at them. There are three such blocks, so Memory Shared Common is 12 KB.

Memory Shared is concerned with guest physical memory and looks at the origin of the arrows. Memory Shared Common, however, deals with machine memory and looks at the destination of the arrows.

The memory metrics that measure guest physical memory and machine memory might appear contradictory. In fact, they are measuring different aspects of a virtual machine's memory usage. By understanding the differences between these metrics, you can better utilize them to diagnose performance issues.

Memory Reliability

Memory reliability, also known as error insolation, allows ESXi to stop using parts of memory when it determines that a failure might occur, as well as when a failure did occur.

Chapter 6 Administering Memory Resources

When enough corrected errors are reported at a particular address, ESXi stops using this address to prevent the corrected error from becoming an uncorrected error.

Memory reliability provides a better VMkernel reliability despite corrected and uncorrected errors in RAM. It also enables the system to avoid using memory pages that might contain errors.

Correcting an Error Isolation Notification

With memory reliability, VMkernel stops using pages that receive an error isolation notification.

The user receives an event in the vSphere Web Client when VMkernel recovers from an uncorrectable memory error, when VMkernel retires a significant percentage of system memory due to a large number of correctable errors, or if there is a large number of pages that are unable to retire.

Procedure

1 Vacate the host.

2 Migrate the virtual machines.

3 Run memory related hardware tests.

About System Swap

System swap is a memory reclamation process that can take advantage of unused memory resources across an entire system.

System swap allows the system to reclaim memory from memory consumers that are not virtual machines. When system swap is enabled you have a tradeoff between the impact of reclaiming the memory from another process and the ability to assign the memory to a virtual machine that can use it. The amount of space required for the system swap is 1GB.

Memory is reclaimed by taking data out of memory and writing it to background storage. Accessing the data from background storage is slower than accessing data from memory, so it is important to carefully select where to store the swapped data.

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vSphere Resource Management

ESXi determines automatically where the system swap should be stored, this is the Preferred swap file location. This decision can be aided by selecting a certain set of options. The system selects the best possible

enabled option. If none of the options are feasible then system swap is not activated.

The available options are:

Datastore - Allow the use of the datastore specified. Please note that a vSAN datastore or a VVol

datastore cannot be specified for system swap files.

Host Swap Cache - Allow the use of part of the host swap cache.

Preferred swap file location - Allow the use of the preferred swap file location configured for the host.

Configure System Swap

You can customize the options that determine the system swap location.

Prerequisites

Select the Enabled check box in the Edit System Swap Settings dialog box.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab.

3 Click Settings, and click System Swap.

4 Click Edit.

5 Select the check boxes for each option that you want to enable.

6 If you select the datastore option, select a datastore from the drop-down menu.

7 Click OK.

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View Graphics Information 7

You can access information about host graphics hardware capability for multiple virtual machines. You can view information about the graphics card and view the virtual machines that use the graphics card.

Virtual machines are listed only if they are turned on and if the graphics card is of the shared type.

Prerequisites

Verify that the virtual machines are turned on.

Procedure

1 In the vSphere Web Client, navigate to the host.

2 Click the Manage tab and click Settings.

3 Under Hardware, select Graphics, and select the graphics card to view the virtual machines that use it.

You can view the name of the graphics card, the vendor, and the total memory allocated to the card.

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vSphere Resource Management

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Managing Storage I/O Resources 8

vSphere Storage I/O Control allows cluster-wide storage I/O prioritization, which allows better workload consolidation and helps reduce extra costs associated with over provisioning.

Storage I/O Control extends the constructs of shares and limits to handle storage I/O resources. You can control the amount of storage I/O that is allocated to virtual machines during periods of I/O congestion, which ensures that more important virtual machines get preference over less important virtual machines for I/O resource allocation.

When you enable Storage I/O Control on a datastore, ESXi begins to monitor the device latency that hosts observe when communicating with that datastore. When device latency exceeds a threshold, the datastore is considered to be congested and each virtual machine that accesses that datastore is allocated I/O resources in proportion to their shares. You set shares per virtual machine. You can adjust the number for each based on need.

Configuring Storage I/O Control is a two-step process:

1 Enable Storage I/O Control for the datastore.

2 Set the number of storage I/O shares and upper limit of I/O operations per second (IOPS) allowed for

each virtual machine.

By default, all virtual machine shares are set to Normal (1000) with unlimited IOPS.

NOTE Storage I/O Control is enabled by default on Storage DRS-enabled datastore clusters.

This chapter includes the following topics:

“Storage I/O Control Requirements,” on page 49

“Storage I/O Control Resource Shares and Limits,” on page 50

“Set Storage I/O Control Resource Shares and Limits,” on page 51

“Enable Storage I/O Control,” on page 51

“Set Storage I/O Control Threshold Value,” on page 52

“Storage DRS Integration with Storage Profiles,” on page 53

Storage I/O Control Requirements

Storage I/O Control has several requirements and limitations.

Datastores that are Storage I/O Control-enabled must be managed by a single vCenter Server system.

Storage I/O Control is supported on Fibre Channel-connected, iSCSI-connected, and NFS-connected

storage. Raw Device Mapping (RDM) is not supported.

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vSphere Resource Management

Storage I/O Control does not support datastores with multiple extents.

Before using Storage I/O Control on datastores that are backed by arrays with automated storage tiering

capabilities, check the VMware Storage/SAN Compatibility Guide to verify whether your automated tiered storage array has been certified to be compatible with Storage I/O Control.

Automated storage tiering is the ability of an array (or group of arrays) to migrate LUNs/volumes or parts of LUNs/volumes to different types of storage media (SSD, FC, SAS, SATA) based on user-set policies and current I/O patterns. No special certification is required for arrays that do not have these automatic migration/tiering features, including those that provide the ability to manually migrate data between different types of storage media.

Storage I/O Control Resource Shares and Limits

You allocate the number of storage I/O shares and upper limit of I/O operations per second (IOPS) allowed for each virtual machine. When storage I/O congestion is detected for a datastore, the I/O workloads of the virtual machines accessing that datastore are adjusted according to the proportion of virtual machine shares each virtual machine has.

Storage I/O shares are similar to those used for memory and CPU resource allocation, which are described in “Resource Allocation Shares,” on page 13. These shares represent the relative importance of a virtual machine with regard to the distribution of storage I/O resources. Under resource contention, virtual machines with higher share values have greater access to the storage array. When you allocate storage I/O resources, you can limit the IOPS that are allowed for a virtual machine. By default, these are unlimited.

The benefits and drawbacks of setting resource limits are described in “Resource Allocation Limit,” on page 14. If the limit you want to set for a virtual machine is in terms of MB per second instead of IOPS, you can convert MB per second into IOPS based on the typical I/O size for that virtual machine. For example, to restrict a backup application with 64KB IOs to 10MB per second, set a limit of 160 IOPS.

View Storage I/O Control Shares and Limits

You can view the shares and limits for all virtual machines running on a datastore. Viewing this information allows you to compare the settings of all virtual machines that are accessing the datastore, regardless of the cluster in which they are running.

Procedure

1 Browse to the datastore in the vSphere Web Client navigator.

2 Under the Related Objects tab, click the Virtual Machines tab.

The tab displays each virtual machine running on the datastore and the associated shares value, and percentage of datastore shares.

Monitor Storage I/O Control Shares

Use the datastore Performance tab to monitor how Storage I/O Control handles the I/O workloads of the virtual machines accessing a datastore based on their shares.

Datastore performance charts allow you to monitor the following information:

Average latency and aggregated IOPS on the datastore

Latency among hosts

Queue depth among hosts

Read/write IOPS among hosts

Read/write latency among virtual machine disks

Read/write IOPS among virtual machine disks

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Chapter 8 Managing Storage I/O Resources

Procedure

1 Browse to the datastore in the vSphere Web Client navigator.

2 Under the Monitor tab, click the Performance tab

3 From the View drop-down menu, select Performance.

For more information, see the vSphere Monitoring and Performance documentation.

Set Storage I/O Control Resource Shares and Limits

Allocate storage I/O resources to virtual machines based on importance by assigning a relative amount of shares to the virtual machine.

Unless virtual machine workloads are very similar, shares do not necessarily dictate allocation in terms of I/O operations or megabytes per second. Higher shares allow a virtual machine to keep more concurrent I/O operations pending at the storage device or datastore compared to a virtual machine with lower shares. Two virtual machines might experience different throughput based on their workloads.

Procedure

1 Find the virtual machine in the vSphere Web Client inventory.

a To find a virtual machine, select a data center, folder, cluster, resource pool, or host.

b Click the Related Objects tab and click Virtual Machines.

2 Right-click the virtual machine and click Edit Settings.

3 Click the Virtual Hardware tab and expand Hard disk.

4 Select a virtual hard disk from the list.

5 Under Shares, click the drop-down menu and select the relative amount of shares to allocate to the

virtual machine (Low, Normal, or High).

You can select Custom to enter a user-defined shares value.

6 Under Limit - IOPS, click the drop-down menu and enter the upper limit of storage resources to

allocate to the virtual machine.

IOPS are the number of I/O operations per second. By default, IOPS are unlimited. You select Low (500), Normal (1000), or High (2000), or you can select Custom to enter a user-defined number of shares.

7 Click OK.

Shares and limits are reflected under Related Objects on the Virtual Machines tab for the host and cluster.

Enable Storage I/O Control

When you enable Storage I/O Control, ESXi monitors datastore latency and throttles the I/O load if the datastore average latency exceeds the threshold.

Procedure

1 Browse to the datastore in the vSphere Web Client navigator.

2 Click the Manage tab.

3 Click Settings and click General.

4 Click Edit for Datastore Capabilities.

5 Select the Enable Storage I/O Control check box.

6 Click OK.

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vSphere Resource Management

Under Datastore Capabilities, Storage I/O Control is enabled for the datastore.

Set Storage I/O Control Threshold Value

The congestion threshold value for a datastore is the upper limit of latency that is allowed for a datastore before Storage I/O Control begins to assign importance to the virtual machine workloads according to their shares.

You do not need to adjust the threshold setting in most environments.

CAUTION Storage I/O Control will not function correctly if you share the same spindles on two different datastores.

If you change the congestion threshold setting, set the value based on the following considerations.

A higher value typically results in higher aggregate throughput and weaker isolation. Throttling will

not occur unless the overall average latency is higher than the threshold.

If throughput is more critical than latency, do not set the value too low. For example, for Fibre Channel

disks, a value below 20ms could lower peak disk throughput. A very high value (above 50ms) might allow very high latency without any significant gain in overall throughput.

A lower value will result in lower device latency and stronger virtual machine I/O performance

isolation. Stronger isolation means that the shares controls are enforced more often. Lower device latency translates into lower I/O latency for the virtual machines with the highest shares, at the cost of higher I/O latency experienced by the virtual machines with fewer shares.

A very low value (lower than 20ms) will result in lower device latency and isolation among I/Os at the

potential cost of a decrease in aggregate datastore throughput.

Setting the value extremely high or extremely lowly results in poor isolation.

Prerequisites

Verify that Storage I/O Control is enabled.

Procedure

1 Browse to the datastore in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Click General.

4 Click Edit for Datastore Capabilities.

5 Select the Enable Storage I/O Control check box.

Storage I/O Control automatically sets the latency threshold that corresponds to the estimated latency when the datastore is operating at 90% of its peak throughput.

6 (Optional) Adjust the Congestion Threshold.

Select a value from the Percentage of peak throughput drop-down menu.

The percentage of peak throughput value indicates the estimated latency threshold when the datastore is using that percentage of its estimated peak throughput.

Select a value from the Manual drop-down menu.

The value must be between 5ms and 100ms. Setting improper congestion threshold values can be detrimental to the performance of the virtual machines on the datastore.

7 (Optional) Click Reset to defaults to restore the congestion threshold setting to the default value

(30ms).

52 VMware, Inc.

Storage DRS Integration with Storage Profiles

Storage Policy Based Management (SPBM) allows you to specify the policy for a virtual machine which is enforced by Storage DRS. A datastore cluster can have set of datastores with different capability profiles. If the virtual machines have storage profiles associated with them, Storage DRS can enforce placement based on underlying datastore capabilities.

As part of Storage DRS integration with storage profiles, the Storage DRS cluster level advanced option

EnforceStorageProfiles is introduced. Advanced option EnforceStorageProfiles takes one of these integer

values: 0,1 or 2. The default value is 0. When the option is set to 0, it indicates that there is no storage profile or policy enforcement on the Storage DRS cluster. When the option is set to 1, it indicates that there is a storage profile or policy soft enforcement on the Storage DRS cluster. This is analogous with DRS soft rules. Storage DRS will comply with storage profile or policy in the optimum level. Storage DRS will violate the storage profile compliant if it is required to do so. Storage DRS affinity rules will have higher precedence over storage profiles only when storage profile enforcement is set to 1. When the option is set to 2, it indicates that there is a storage profile or policy hard enforcement on the Storage DRS cluster. This is analogous with DRS hard rules. Storage DRS will not violate the storage profile or policy compliant. Storage profiles will have higher precedence over affinity rules. Storage DRS will generate fault: could not fix

anti-affinity rule violation

Prerequisites

Chapter 8 Managing Storage I/O Resources

By default, Storage DRS will not enforce storage policies associated with a virtual machine. Please configure

EnforceStorageProfiles option according to your requirements. The options are Default (0), Soft (1) or Hard

(2).

Procedure

1 Log in to the vSphere Web client as an Administrator.

2 In the vSphere Web Client, click on the Storage DRS cluster, then select Manage > Settings > Storage

DRS.

3 Click Edit > Advanced Options > Configuration parameters and select Add.

4 Click in the area under the Option heading and type EnforceStorageProfiles

5 Click in the area under the Value heading to the right of the previously entered advanced option name

and type the value of either 0, 1 or 2.

6 Click OK.

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Managing Resource Pools 9

root resource pool

siblings

parent resource pool child resource pool

A resource pool is a logical abstraction for flexible management of resources. Resource pools can be grouped into hierarchies and used to hierarchically partition available CPU and memory resources.

Each standalone host and each DRS cluster has an (invisible) root resource pool that groups the resources of that host or cluster. The root resource pool does not appear because the resources of the host (or cluster) and the root resource pool are always the same.

Users can create child resource pools of the root resource pool or of any user-created child resource pool. Each child resource pool owns some of the parent’s resources and can, in turn, have a hierarchy of child resource pools to represent successively smaller units of computational capability.

A resource pool can contain child resource pools, virtual machines, or both. You can create a hierarchy of shared resources. The resource pools at a higher level are called parent resource pools. Resource pools and virtual machines that are at the same level are called siblings. The cluster itself represents the root resource pool. If you do not create child resource pools, only the root resource pools exist.

In the following example, RP-QA is the parent resource pool for RP-QA-UI. RP-Marketing and RP-QA are siblings. The three virtual machines immediately below RP-Marketing are also siblings.

Figure 9‑1. Parents, Children, and Siblings in Resource Pool Hierarchy

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For each resource pool, you specify reservation, limit, shares, and whether the reservation should be expandable. The resource pool resources are then available to child resource pools and virtual machines.

This chapter includes the following topics:

“Why Use Resource Pools?,” on page 56

“Create a Resource Pool,” on page 57

“Edit a Resource Pool,” on page 58

“Add a Virtual Machine to a Resource Pool,” on page 58

“Remove a Virtual Machine from a Resource Pool,” on page 59

“Remove a Resource Pool,” on page 60

“Resource Pool Admission Control,” on page 60

VM-QA 1 VM-QA 2

6GHz, 3GB

4GHz, 2GB 2GHz, 1GB

RP-QA

VM-Marketing 1 VM-Marketing 2 VM-Marketing 3

RP-

Marketing

host

vSphere Resource Management

Why Use Resource Pools?

Resource pools allow you to delegate control over resources of a host (or a cluster), but the benefits are evident when you use resource pools to compartmentalize all resources in a cluster. Create multiple resource pools as direct children of the host or cluster and configure them. You can then delegate control over the resource pools to other individuals or organizations.

Using resource pools can result in the following benefits.

Flexible hierarchical organization—Add, remove, or reorganize resource pools or change resource

allocations as needed.

Isolation between pools, sharing within pools—Top-level administrators can make a pool of resources

available to a department-level administrator. Allocation changes that are internal to one departmental resource pool do not unfairly affect other unrelated resource pools.

Access control and delegation—When a top-level administrator makes a resource pool available to a

department-level administrator, that administrator can then perform all virtual machine creation and management within the boundaries of the resources to which the resource pool is entitled by the current shares, reservation, and limit settings. Delegation is usually done in conjunction with permissions settings.

Separation of resources from hardware—If you are using clusters enabled for DRS, the resources of all

hosts are always assigned to the cluster. That means administrators can perform resource management independently of the actual hosts that contribute to the resources. If you replace three 2GB hosts with two 3GB hosts, you do not need to make changes to your resource allocations.

This separation allows administrators to think more about aggregate computing capacity and less about individual hosts.

Management of sets of virtual machines running a multitier service— Group virtual machines for a

multitier service in a resource pool. You do not need to set resources on each virtual machine. Instead, you can control the aggregate allocation of resources to the set of virtual machines by changing settings on their enclosing resource pool.

For example, assume a host has a number of virtual machines. The marketing department uses three of the virtual machines and the QA department uses two virtual machines. Because the QA department needs larger amounts of CPU and memory, the administrator creates one resource pool for each group. The administrator sets CPU Shares to High for the QA department pool and to Normal for the Marketing department pool so that the QA department users can run automated tests. The second resource pool with fewer CPU and memory resources is sufficient for the lighter load of the marketing staff. Whenever the QA department is not fully using its allocation, the marketing department can use the available resources.

The numbers in the following figure show the effective allocations to the resource pools.

Figure 9‑2. Allocating Resources to Resource Pools

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Create a Resource Pool

You can create a child resource pool of any ESXi host, resource pool, or DRS cluster.

NOTE If a host has been added to a cluster, you cannot create child resource pools of that host. If the cluster is enabled for DRS, you can create child resource pools of the cluster.

When you create a child resource pool, you are prompted for resource pool attribute information. The system uses admission control to make sure you cannot allocate resources that are not available.

Prerequisites

The vSphere Web Client is connected to the vCenter Server system.

Procedure

1 In the vSphere Web Client navigator, select a parent object for the resource pool (a host, another

resource pool, or a DRS cluster).

2 Right-click the object and select New Resource Pool.

3 Type a name to identify the resource pool.

4 Specify how to allocate CPU and memory resources.

Chapter 9 Managing Resource Pools

The CPU resources for your resource pool are the guaranteed physical resources the host reserves for a resource pool. Normally, you accept the default and let the host handle resource allocation.

Option Description

Reservation

Expandable Reservation

Limit

Specify shares for this resource pool with respect to the parent’s total resources. Sibling resource pools share resources according to their relative share values bounded by the reservation and limit.

Select Low, Normal, or High to specify share values respectively in a

1:2:4 ratio.

Select Custom to give each virtual machine a specific number of

shares, which expresses a proportional weight.

Specify a guaranteed CPU or memory allocation for this resource pool. Defaults to 0.

A nonzero reservation is subtracted from the unreserved resources of the parent (host or resource pool). The resources are considered reserved, regardless of whether virtual machines are associated with the resource pool.

When the check box is selected (default), expandable reservations are considered during admission control.

If you power on a virtual machine in this resource pool, and the combined reservations of the virtual machines are larger than the reservation of the resource pool, the resource pool can use resources from its parent or ancestors.

Specify the upper limit for this resource pool’s CPU or memory allocation. You can usually accept the default (Unlimited).

To specify a limit, deselect the Unlimited check box.

5 Click OK.

After you create a resource pool, you can add virtual machines to it. A virtual machine’s shares are relative to other virtual machines (or resource pools) with the same parent resource pool.

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Example: Creating Resource Pools

Assume that you have a host that provides 6GHz of CPU and 3GB of memory that must be shared between your marketing and QA departments. You also want to share the resources unevenly, giving one department (QA) a higher priority. This can be accomplished by creating a resource pool for each department and using the Shares attribute to prioritize the allocation of resources.

The example shows how to create a resource pool with the ESXi host as the parent resource.

1 In the Create Resource Pool dialog box, type a name for the QA department’s resource pool (for

example, RP-QA).

2 Specify Shares of High for the CPU and memory resources of RP-QA.

3 Create a second resource pool, RP-Marketing.

Leave Shares at Normal for CPU and memory.

4 Click OK.

If there is resource contention, RP-QA receives 4GHz and 2GB of memory, and RP-Marketing 2GHz and 1GB. Otherwise, they can receive more than this allotment. Those resources are then available to the virtual machines in the respective resource pools.

Edit a Resource Pool

After you create the resource pool, you can edit its CPU and memory resource settings.

Procedure

1 Browse to the resource pool in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 (Optional) You can change all attributes of the selected resource pool as described in “Create a Resource

Pool,” on page 57.

Under CPU Resources, click Edit to change CPU resource settings.

Under Memory Resources, click Edit to change memory resource settings.

4 Click OK to save your changes.

Add a Virtual Machine to a Resource Pool

When you create a virtual machine, you can specify a resource pool location as part of the creation process. You can also add an existing virtual machine to a resource pool.

When you move a virtual machine to a new resource pool:

The virtual machine’s reservation and limit do not change.

If the virtual machine’s shares are high, medium, or low, %Shares adjusts to reflect the total number of

shares in use in the new resource pool.

If the virtual machine has custom shares assigned, the share value is maintained.

NOTE Because share allocations are relative to a resource pool, you might have to manually change a virtual machine’s shares when you move it into a resource pool so that the virtual machine’s shares are consistent with the relative values in the new resource pool. A warning appears if a virtual machine would receive a very large (or very small) percentage of total shares.

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Chapter 9 Managing Resource Pools

Under Monitor, the information displayed in the Resource Reservation tab about the resource pool’s

reserved and unreserved CPU and memory resources changes to reflect the reservations associated with the virtual machine (if any).

NOTE If a virtual machine has been powered off or suspended, it can be moved but overall available resources (such as reserved and unreserved CPU and memory) for the resource pool are not affected.

Procedure

1 Find the virtual machine in the vSphere Web Client inventory.

a To find a virtual machine, select a data center, folder, cluster, resource pool, or host.

b Click the Related Objects tab and click Virtual Machines.

2 Right-click the virtual machine and click Migrate.

You can move the virtual machine to another host.

You can move the virtual machine's storage to another datastore.

You can move the virtual machine to another host and move its storage to another datastore.

3 Select a resource pool in which to run the virtual machine.

4 Review your selections and click Finish.

If a virtual machine is powered on, and the destination resource pool does not have enough CPU or memory to guarantee the virtual machine’s reservation, the move fails because admission control does not allow it. An error dialog box displays available and requested resources, so you can consider whether an adjustment might resolve the issue.

Remove a Virtual Machine from a Resource Pool

You can remove a virtual machine from a resource pool either by moving the virtual machine to another resource pool or deleting it.

When you remove a virtual machine from a resource pool, the total number of shares associated with the resource pool decreases, so that each remaining share represents more resources. For example, assume you have a pool that is entitled to 6GHz, containing three virtual machines with shares set to Normal. Assuming the virtual machines are CPU-bound, each gets an equal allocation of 2GHz. If one of the virtual machines is moved to a different resource pool, the two remaining virtual machines each receive an equal allocation of 3GHz.

Procedure

1 Browse to the resource pool in the vSphere Web Client navigator.

2 Choose one of the following methods to remove the virtual machine from a resource pool.

Right-click the virtual machine and select Migrate to move the virtual machine to another resource

pool.

You do not need to power off the virtual machine before you move it.

Right-click the virtual machine and select Delete.

You must power off the virtual machine before you can completely remove it.

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Remove a Resource Pool

You can remove a resource pool from the inventory.

Procedure

1 In the vSphere Web Client, right-click the resource pool and Select Delete.

A confirmation dialog box appears.

2 Click Yes to remove the resource pool.

Resource Pool Admission Control

When you power on a virtual machine in a resource pool, or try to create a child resource pool, the system performs additional admission control to ensure the resource pool’s restrictions are not violated.

Before you power on a virtual machine or create a resource pool, ensure that sufficient resources are available using the Resource Reservation tab in the vSphere Web Client. The Available Reservation value for CPU and memory displays resources that are unreserved.

How available CPU and memory resources are computed and whether actions are performed depends on the Reservation Type.

Table 9‑1. Reservation Types

Reservation Type Description

Fixed The system checks whether the selected resource pool has sufficient unreserved

resources. If it does, the action can be performed. If it does not, a message appears and the action cannot be performed.

Expandable

(default)

The system considers the resources available in the selected resource pool and its direct parent resource pool. If the parent resource pool also has the Expandable Reservation option selected, it can borrow resources from its parent resource pool. Borrowing resources occurs recursively from the ancestors of the current resource pool as long as the Expandable Reservation option is selected. Leaving this option selected offers more flexibility, but, at the same time provides less protection. A child resource pool owner might reserve more resources than you anticipate.

The system does not allow you to violate preconfigured Reservation or Limit settings. Each time you reconfigure a resource pool or power on a virtual machine, the system validates all parameters so all servicelevel guarantees can still be met.

Expandable Reservations Example 1

This example shows you how a resource pool with expandable reservations works.

Assume an administrator manages pool P, and defines two child resource pools, S1 and S2, for two different users (or groups).

The administrator knows that users want to power on virtual machines with reservations, but does not know how much each user will need to reserve. Making the reservations for S1 and S2 expandable allows the administrator to more flexibly share and inherit the common reservation for pool P.

Without expandable reservations, the administrator needs to explicitly allocate S1 and S2 a specific amount. Such specific allocations can be inflexible, especially in deep resource pool hierarchies and can complicate setting reservations in the resource pool hierarchy.

Expandable reservations cause a loss of strict isolation. S1 can start using all of P's reservation, so that no memory or CPU is directly available to S2.

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Expandable Reservations Example 2

VM-K1, 2GHz VM-K2, 2GHz

2GHz

6GHz

RP-KID

VM-M1, 1GHz

RP-MOM

VM-K1, 2GHz VM-K2, 2GHz

2GHz

6GHz

RP-KID

VM-M1, 1GHz VM-M2, 2GHz

RP-MOM

This example shows how a resource pool with expandable reservations works.

Assume the following scenario, as shown in the figure.

Parent pool RP-MOM has a reservation of 6GHz and one running virtual machine VM-M1 that reserves

1GHz.

You create a child resource pool RP-KID with a reservation of 2GHz and with Expandable Reservation

selected.

You add two virtual machines, VM-K1 and VM-K2, with reservations of 2GHz each to the child

resource pool and try to power them on.

VM-K1 can reserve the resources directly from RP-KID (which has 2GHz).

No local resources are available for VM-K2, so it borrows resources from the parent resource pool, RP-

MOM. RP-MOM has 6GHz minus 1GHz (reserved by the virtual machine) minus 2GHz (reserved by RP-KID), which leaves 3GHz unreserved. With 3GHz available, you can power on the 2GHz virtual machine.

Figure 9‑3. Admission Control with Expandable Resource Pools: Successful Power-On

Chapter 9 Managing Resource Pools

Now, consider another scenario with VM-M1 and VM-M2.

Power on two virtual machines in RP-MOM with a total reservation of 3GHz.

You can still power on VM-K1 in RP-KID because 2GHz are available locally.

When you try to power on VM-K2, RP-KID has no unreserved CPU capacity so it checks its parent. RP-

MOM has only 1GHz of unreserved capacity available (5GHz of RP-MOM are already in use—3GHz reserved by the local virtual machines and 2GHz reserved by RP-KID). As a result, you cannot power on VM-K2, which requires a 2GHz reservation.

Figure 9‑4. Admission Control with Expandable Resource Pools: Power-On Prevented

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Creating a DRS Cluster 10

A cluster is a collection of ESXi hosts and associated virtual machines with shared resources and a shared management interface. Before you can obtain the benefits of cluster-level resource management you must create a cluster and enable DRS.

Depending on whether or not Enhanced vMotion Compatibility (EVC) is enabled, DRS behaves differently when you use vSphere Fault Tolerance (vSphere FT) virtual machines in your cluster.

Table 10‑1. DRS Behavior with vSphere FT Virtual Machines and EVC

EVC DRS (Load Balancing) DRS (Initial Placement)

Enabled Enabled (Primary and Secondary VMs) Enabled (Primary and Secondary VMs)

Disabled Disabled (Primary and Secondary VMs) Disabled (Primary VMs)

Fully Automated (Secondary VMs)

This chapter includes the following topics:

“Admission Control and Initial Placement,” on page 64

“Virtual Machine Migration,” on page 65

“DRS Cluster Requirements,” on page 67

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“Configuring DRS with Virtual Flash,” on page 68

“Create a Cluster,” on page 68

“Edit a Cluster,” on page 69

“Create a DRS Cluster,” on page 70

“Set a Custom Automation Level for a Virtual Machine,” on page 71

“Disable DRS,” on page 72

“Restore a Resource Pool Tree,” on page 72

vSphere Resource Management

Admission Control and Initial Placement

When you attempt to power on a single virtual machine or a group of virtual machines in a DRS-enabled cluster, vCenter Server performs admission control. It checks that there are enough resources in the cluster to support the virtual machine(s).

If the cluster does not have sufficient resources to power on a single virtual machine, or any of the virtual machines in a group power-on attempt, a message appears. Otherwise, for each virtual machine, DRS generates a recommendation of a host on which to run the virtual machine and takes one of the following actions

Automatically executes the placement recommendation.

Displays the placement recommendation, which the user can then choose to accept or override.

NOTE No initial placement recommendations are given for virtual machines on standalone hosts or in non-DRS clusters. When powered on, they are placed on the host where they currently reside.

Single Virtual Machine Power On

In a DRS cluster, you can power on a single virtual machine and receive initial placement recommendations.

When you power on a single virtual machine, you have two types of initial placement recommendations:

A single virtual machine is being powered on and no prerequisite steps are needed.

The user is presented with a list of mutually exclusive initial placement recommendations for the virtual machine. You can select only one.

A single virtual machine is being powered on, but prerequisite actions are required.

These actions include powering on a host in standby mode or the migration of other virtual machines from one host to another. In this case, the recommendations provided have multiple lines, showing each of the prerequisite actions. The user can either accept this entire recommendation or cancel powering on the virtual machine.

Group Power On

You can attempt to power on multiple virtual machines at the same time (group power on).

Virtual machines selected for a group power-on attempt do not have to be in the same DRS cluster. They can be selected across clusters but must be within the same data center. It is also possible to include virtual machines located in non-DRS clusters or on standalone hosts. These are powered on automatically and not included in any initial placement recommendation.

The initial placement recommendations for group power-on attempts are provided on a per-cluster basis. If all of the placement-related actions for a group power-on attempt are in automatic mode, the virtual machines are powered on with no initial placement recommendation given. If placement-related actions for any of the virtual machines are in manual mode, the powering on of all of the virtual machines (including those that are in automatic mode) is manual and is included in an initial placement recommendation.

For each DRS cluster that the virtual machines being powered on belong to, there is a single recommendation, which contains all of the prerequisites (or no recommendation). All such cluster-specific recommendations are presented together under the Power On Recommendations tab.

When a nonautomatic group power-on attempt is made, and virtual machines not subject to an initial placement recommendation (that is, those on standalone hosts or in non-DRS clusters) are included, vCenter Server attempts to power them on automatically. If these power ons are successful, they are listed under the Started Power-Ons tab. Any virtual machines that fail to power on are listed under the Failed Power-Ons tab.

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Example: Group Power On

Host 1

VM1

VM4

VM2 VM3

VM5 VM6

Host 2

VM7

Host 3

VM8 VM9

Host 1

VM1 VM2 VM3

Host 2

VM7 VM4 VM5

Host 3

VM8 VM9 VM6

The user selects three virtual machines in the same data center for a group power-on attempt. The first two virtual machines (VM1 and VM2) are in the same DRS cluster (Cluster1), while the third virtual machine (VM3) is on a standalone host. VM1 is in automatic mode and VM2 is in manual mode. For this scenario, the user is presented with an initial placement recommendation for Cluster1 (under the Power On Recommendations tab) which consists of actions for powering on VM1 and VM2. An attempt is made to power on VM3 automatically and, if successful, it is listed under the Started Power-Ons tab. If this attempt fails, it is listed under the Failed Power-Ons tab.

Virtual Machine Migration

Although DRS performs initial placements so that load is balanced across the cluster, changes in virtual machine load and resource availability can cause the cluster to become unbalanced. To correct such imbalances, DRS generates migration recommendations.

If DRS is enabled on the cluster, load can be distributed more uniformly to reduce the degree of this imbalance. For example, the three hosts on the left side of the following figure are unbalanced. Assume that Host 1, Host 2, and Host 3 have identical capacity, and all virtual machines have the same configuration and load (which includes reservation, if set). However, because Host 1 has six virtual machines, its resources might be overused while ample resources are available on Host 2 and Host 3. DRS migrates (or recommends the migration of) virtual machines from Host 1 to Host 2 and Host 3. On the right side of the diagram, the properly load balanced configuration of the hosts that results appears.

Chapter 10 Creating a DRS Cluster

Figure 10‑1. Load Balancing

When a cluster becomes unbalanced, DRS makes recommendations or migrates virtual machines, depending on the default automation level:

If the cluster or any of the virtual machines involved are manual or partially automated, vCenter Server

does not take automatic actions to balance resources. Instead, the Summary page indicates that migration recommendations are available and the DRS Recommendations page displays recommendations for changes that make the most efficient use of resources across the cluster.

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If the cluster and virtual machines involved are all fully automated, vCenter Server migrates running

virtual machines between hosts as needed to ensure efficient use of cluster resources.

NOTE Even in an automatic migration setup, users can explicitly migrate individual virtual machines, but vCenter Server might move those virtual machines to other hosts to optimize cluster resources.

By default, automation level is specified for the whole cluster. You can also specify a custom automation level for individual virtual machines.

DRS Migration Threshold

The DRS migration threshold allows you to specify which recommendations are generated and then applied (when the virtual machines involved in the recommendation are in fully automated mode) or shown (if in manual mode). This threshold is also a measure of how much cluster imbalance across host (CPU and memory) loads is acceptable.

You can move the threshold slider to use one of five settings, ranging from Conservative to Aggressive. The five migration settings generate recommendations based on their assigned priority level. Each setting you move the slider to the right allows the inclusion of one more lower level of priority. The Conservative setting generates only priority-one recommendations (mandatory recommendations), the next level to the right generates priority-two recommendations and higher, and so on, down to the Aggressive level which generates priority-five recommendations and higher (that is, all recommendations.)

A priority level for each migration recommendation is computed using the load imbalance metric of the cluster. This metric is displayed as Current host load standard deviation in the cluster's Summary tab in the vSphere Web Client. A higher load imbalance leads to higher-priority migration recommendations. For more information about this metric and how a recommendation priority level is calculated, see the VMware Knowledge Base article "Calculating the priority level of a VMware DRS migration recommendation."

After a recommendation receives a priority level, this level is compared to the migration threshold you set. If the priority level is less than or equal to the threshold setting, the recommendation is either applied (if the relevant virtual machines are in fully automated mode) or displayed to the user for confirmation (if in manual or partially automated mode.)

Migration Recommendations

If you create a cluster with a default manual or partially automated mode, vCenter Server displays migration recommendations on the DRS Recommendations page.

The system supplies as many recommendations as necessary to enforce rules and balance the resources of the cluster. Each recommendation includes the virtual machine to be moved, current (source) host and destination host, and a reason for the recommendation. The reason can be one of the following:

Balance average CPU loads or reservations.

Balance average memory loads or reservations.

Satisfy resource pool reservations.

Satisfy an affinity rule.

Host is entering maintenance mode or standby mode.

NOTE If you are using the vSphere Distributed Power Management (DPM) feature, in addition to migration recommendations, DRS provides host power state recommendations.

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DRS Cluster Requirements

Hosts that are added to a DRS cluster must meet certain requirements to use cluster features successfully.

Shared Storage Requirements

A DRS cluster has certain shared storage requirements.

Ensure that the managed hosts use shared storage. Shared storage is typically on a SAN, but can also be implemented using NAS shared storage.

See the vSphere Storage documentation for information about other shared storage.

Shared VMFS Volume Requirements

A DRS cluster has certain shared VMFS volume requirements.

Configure all managed hosts to use shared VMFS volumes.

Place the disks of all virtual machines on VMFS volumes that are accessible by source and destination

hosts.

Ensure the VMFS volume is sufficiently large to store all virtual disks for your virtual machines.

Chapter 10 Creating a DRS Cluster

Ensure all VMFS volumes on source and destination hosts use volume names, and all virtual machines

use those volume names for specifying the virtual disks.

NOTE Virtual machine swap files also need to be on a VMFS accessible to source and destination hosts (just like .vmdk virtual disk files). This requirement does not apply if all source and destination hosts are ESX Server 3.5 or higher and using host-local swap. In that case, vMotion with swap files on unshared storage is supported. Swap files are placed on a VMFS by default, but administrators might override the file location using advanced virtual machine configuration options.

Processor Compatibility Requirements

A DRS cluster has certain processor compatibility requirements.

To avoid limiting the capabilities of DRS, you should maximize the processor compatibility of source and destination hosts in the cluster.

vMotion transfers the running architectural state of a virtual machine between underlying ESXi hosts. vMotion compatibility means that the processors of the destination host must be able to resume execution using the equivalent instructions where the processors of the source host were suspended. Processor clock speeds and cache sizes might vary, but processors must come from the same vendor class (Intel versus AMD) and the same processor family to be compatible for migration with vMotion.

Processor families are defined by the processor vendors. You can distinguish different processor versions within the same family by comparing the processors’ model, stepping level, and extended features.

Sometimes, processor vendors have introduced significant architectural changes within the same processor family (such as 64-bit extensions and SSE3). VMware identifies these exceptions if it cannot guarantee successful migration with vMotion.

vCenter Server provides features that help ensure that virtual machines migrated with vMotion meet processor compatibility requirements. These features include:

Enhanced vMotion Compatibility (EVC) – You can use EVC to help ensure vMotion compatibility for

the hosts in a cluster. EVC ensures that all hosts in a cluster present the same CPU feature set to virtual machines, even if the actual CPUs on the hosts differ. This prevents migrations with vMotion from failing due to incompatible CPUs.

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Configure EVC from the Cluster Settings dialog box. The hosts in a cluster must meet certain requirements for the cluster to use EVC. For information about EVC and EVC requirements, see the vCenter Server and Host Management documentation.

CPU compatibility masks – vCenter Server compares the CPU features available to a virtual machine

with the CPU features of the destination host to determine whether to allow or disallow migrations with vMotion. By applying CPU compatibility masks to individual virtual machines, you can hide certain CPU features from the virtual machine and potentially prevent migrations with vMotion from failing due to incompatible CPUs.

vMotion Requirements for DRS Clusters

A DRS cluster has certain vMotion requirements.

To enable the use of DRS migration recommendations, the hosts in your cluster must be part of a vMotion network. If the hosts are not in the vMotion network, DRS can still make initial placement recommendations.

To be configured for vMotion, each host in the cluster must meet the following requirements:

vMotion does not support raw disks or migration of applications clustered using Microsoft Cluster

Service (MSCS).

vMotion requires a private Gigabit Ethernet migration network between all of the vMotion enabled

managed hosts. When vMotion is enabled on a managed host, configure a unique network identity object for the managed host and connect it to the private migration network.

Configuring DRS with Virtual Flash

DRS can manage virtual machines that have virtual flash reservations.

Virtual flash capacity appears as a statistic that is regularly reported from the host to the vSphere Web Client. Each time DRS runs, it uses the most recent capacity value reported.

You can configure one virtual flash resource per host. This means that during virtual machine power-on time, DRS does not need to select between different virtual flash resources on a given host.

DRS selects a host that has sufficient available virtual flash capacity to start the virtual machine. If DRS cannot satisfy the virtual flash reservation of a virtual machine, it cannot be powered-on. DRS treats a powered-on virtual machine with a virtual flash reservation as having a soft affinity with its current host. DRS will not recommend such a virtual machine for vMotion except for mandatory reasons, such as putting a host in maintenance mode, or to reduce the load on an over utilized host.

Create a Cluster

A cluster is a group of hosts. When a host is added to a cluster, the host's resources become part of the cluster's resources. The cluster manages the resources of all hosts within it. Clusters enable the vSphere High Availability (HA) and vSphere Distributed Resource Scheduler (DRS) solutions. You can also enable Virtual SAN on a cluster.

Prerequisites

Verify that you have sufficient permissions to create a cluster object.

Verify that a data center exists in the inventory.

Procedure

1 Browse to a data center in the vSphere Web Client navigator.

2 Right-click the data center and select New Cluster.

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Chapter 10 Creating a DRS Cluster

3 Enter a name for the cluster.

4 Select DRS and vSphere HA cluster features.

Option Description

To use DRS with this cluster

To use HA with this cluster

a Select the DRS Turn ON check box.

b Select an automation level and a migration threshold.

a Select the vSphere HA Turn ON check box.

b Select whether to enable host monitoring and admission control.

c If admission control is enabled, specify a policy.

d Select a VM Monitoring option.

e Specify the virtual machine monitoring sensitivity.

5 Select an Enhanced vMotion Compatibility (EVC) setting.

EVC ensures that all hosts in a cluster present the same CPU feature set to virtual machines, even if the actual CPUs on the hosts differ. This prevents migrations with vMotion from failing due to incompatible CPUs.

6 Enable Virtual SAN.

a Select the Virtual SAN Turn ON check box.

b Specify whether to add disks automatically or manually to the Virtual SAN cluster.

7 Click OK.

The cluster is added to the inventory.

What to do next

Add hosts and resource pools to the cluster.

For information about Virtual SAN and how to use Virtual SAN clusters, see the vSphere Storage publication.

Edit a Cluster

You can enable cluster features and edit settings for existing clusters.

Prerequisites

Required privileges: Host.Inventory.Modify Cluster or Host.Inventory.Remove Cluster or Host.Inventory.Rename Cluster or Host.Inventory.Move Cluster

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Select the Manage tab and click Settings.

3 Under Services select vSphere DRS or vSphere HA and click Edit to edit cluster services.

4 Click OK.

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Create a DRS Cluster

When you add a host to a DRS cluster, the host’s resources become part of the cluster’s resources. In addition to this aggregation of resources, with a DRS cluster you can support cluster-wide resource pools and enforce cluster-level resource allocation policies.

The following cluster-level resource management capabilities are also available.

Load Balancing

The distribution and usage of CPU and memory resources for all hosts and virtual machines in the cluster are continuously monitored. DRS compares these metrics to an ideal resource utilization given the attributes of the cluster’s resource pools and virtual machines, the current demand, and the imbalance target. It then performs (or recommends) virtual machine migrations accordingly. See “Virtual Machine Migration,” on page 65. When you first power on a virtual machine in the cluster, DRS attempts to maintain proper load balancing by either placing the virtual machine on an appropriate host or making a recommendation. See “Admission Control and

Initial Placement,” on page 64.

Power management

When the vSphere Distributed Power Management (DPM) feature is enabled, DRS compares cluster- and host-level capacity to the demands of the cluster’s virtual machines, including recent historical demand. It places (or recommends placing) hosts in standby power mode if sufficient excess capacity is found or powering on hosts if capacity is needed. Depending on the resulting host power state recommendations, virtual machines might need to be migrated to and from the hosts as well. See “Managing Power

Resources,” on page 82.

Affinity Rules

You can control the placement of virtual machines on hosts within a cluster, by assigning affinity rules. See “Using DRS Affinity Rules,” on page 86.

Prerequisites

You can create a cluster without a special license, but you must have a license to enable a cluster for vSphere DRS (or vSphere HA).

Procedure

1 Right-click a data center in the vSphere Web Client and select New Cluster.

2 Name the cluster in the Name text box.

This name appears in the vSphere Web Client navigator.

3 Select the DRS Turn ON check box.

4 Select a default automation level for DRS.

Automation Level Action

Initial placement: Recommended host(s) is displayed.

Manual

Partially Automated

Fully Automated

Migration: Recommendation is displayed.

Initial placement: Automatic.

Migration: Recommendation is displayed.

Initial placement: Automatic.

Migration: Recommendation is executed automatically.

5 Set the migration threshold for DRS.

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6 (Optional) Select the vSphere HA Turn ON check box to enable vSphere HA.

vSphere HA allows you to:

Enable host monitoring.

Enable admission control.

Specify the type of policy that admission control should enforce.

Adjust the monitoring sensitivity of virtual machine monitoring.

7 If appropriate, enable Enhanced vMotion Compatibility (EVC) and select the mode it should operate in.

8 Click OK to complete cluster creation.

A new cluster does not include any hosts or virtual machines.

To add hosts and virtual machines to the cluster see “Adding Hosts to a Cluster,” on page 73.

Set a Custom Automation Level for a Virtual Machine

After you create a DRS cluster, you can customize the automation level for individual virtual machines to override the cluster’s default automation level.

For example, you can select Manual for specific virtual machines in a cluster with full automation, or Partially Automated for specific virtual machines in a manual cluster.

Chapter 10 Creating a DRS Cluster

If a virtual machine is set to Disabled, vCenter Server does not migrate that virtual machine or provide migration recommendations for it. This is known as pinning the virtual machine to its registered host.

NOTE If you have not enabled Enhanced vMotion Compatibility (EVC) for the cluster, fault tolerant virtual machines are set to DRS disabled. They appear on this screen, but you cannot assign an automation mode to them.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Services, select vSphere DRS and click Edit. Expand DRS Automation.

4 Select the Enable individual virtual machine automation levels check box.

5 To temporarily disable any individual virtual machine overrides, deselect the Enable individual virtual

machine automation levels check box.

Virtual machine settings are restored when the check box is selected again.

6 To temporarily suspend all vMotion activity in a cluster, put the cluster in manual mode and deselect

the Enable individual virtual machine automation levels check box.

7 Select one or more virtual machines.

8 Click the Automation Level column and select an automation level from the drop-down menu.

Option Description

Manual

Fully Automated

Partially Automated

Disabled

Placement and migration recommendations are displayed, but do not run until you manually apply the recommendation.

Placement and migration recommendations run automatically.

Initial placement is performed automatically. Migration recommendations are displayed, but do not run.

vCenter Server does not migrate the virtual machine or provide migration recommendations for it.

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9 Click OK.

NOTE Other VMware products or features, such as vSphere vApp and vSphere Fault Tolerance, might

override the automation levels of virtual machines in a DRS cluster. Refer to the product-specific documentation for details.

Disable DRS

You can turn off DRS for a cluster.

When DRS is disabled, the cluster’s resource pool hierarchy and affinity rules are not reestablished when DRS is turned back on. If you disable DRS, the resource pools are removed from the cluster. To avoid losing the resource pools, save a snapshot of the resource pool tree on your local machine. You can use the snapshot to restore the resource pool when you enable DRS.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under vSphere DRS, click Edit.

4 Deselect the Turn On vSphere DRS check box.

5 Click OK to turn off DRS.

6 (Optional) Choose an option to save the resource pool.

Click Yes to save a resource pool tree snapshot on a local machine.

Click No to turn off DRS without saving a resource pool tree snapshot.

Restore a Resource Pool Tree

You can restore a previously saved resource pool tree snapshot.

Prerequisites

vSphere DRS must be turned ON.

You can restore a snapshot only on the same cluster that it was taken.

No other resource pools are present in the cluster.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Right-click on the cluster and select Restore Resource Pool Tree.

3 Click Browse, and locate the snapshot file on your local machine.

4 Click Open.

5 Click OK to restore the resource pool tree.

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Using DRS Clusters to Manage

Resources 11

After you create a DRS cluster, you can customize it and use it to manage resources.

To customize your DRS cluster and the resources it contains you can configure affinity rules and you can add and remove hosts and virtual machines. When a cluster’s settings and resources have been defined, you should ensure that it is and remains a valid cluster. You can also use a valid DRS cluster to manage power resources and interoperate with vSphere HA.

This chapter includes the following topics:

“Adding Hosts to a Cluster,” on page 73

“Adding Virtual Machines to a Cluster,” on page 75

“Removing Virtual Machines from a Cluster,” on page 75

“Removing a Host from a Cluster,” on page 76

“DRS Cluster Validity,” on page 77

“Managing Power Resources,” on page 82

“Using DRS Affinity Rules,” on page 86

Adding Hosts to a Cluster

The procedure for adding hosts to a cluster is different for hosts managed by the same vCenter Server (managed hosts) than for hosts not managed by that server.

After a host has been added, the virtual machines deployed to the host become part of the cluster and DRS can recommend migration of some virtual machines to other hosts in the cluster.

Add a Managed Host to a Cluster

When you add a standalone host already being managed by vCenter Server to a DRS cluster, the host’s resources become associated with the cluster.

You can decide whether you want to associate existing virtual machines and resource pools with the cluster’s root resource pool or graft the resource pool hierarchy.

NOTE If a host has no child resource pools or virtual machines, the host’s resources are added to the cluster but no resource pool hierarchy with a top-level resource pool is created.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Right-click the host and select Move To.

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vSphere Resource Management

3 Select a cluster.

4 Click OK to apply the changes.

5 Select what to do with the host’s virtual machines and resource pools.

Put this host’s virtual machines in the cluster’s root resource pool

vCenter Server removes all existing resource pools of the host and the virtual machines in the host’s hierarchy are all attached to the root. Because share allocations are relative to a resource pool, you might have to manually change a virtual machine’s shares after selecting this option, which destroys the resource pool hierarchy.

Create a resource pool for this host’s virtual machines and resource pools

vCenter Server creates a top-level resource pool that becomes a direct child of the cluster and adds all children of the host to that new resource pool. You can supply a name for that new top-level resource pool. The default is Grafted from <host_name>.

The host is added to the cluster.

Add an Unmanaged Host to a Cluster

You can add an unmanaged host to a cluster. Such a host is not currently managed by the same vCenter Server system as the cluster and it is not visible in the vSphere Web Client.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Right-click the cluster and select Add Host.

3 Enter the host name, user name, and password, and click Next.

4 View the summary information and click Next.

5 Assign an existing or a new license key and click Next.

6 (Optional) You can enable lockdown mode to prevent remote users from logging directly into the host.

If you do not enable lockdown mode, you can configure this option later by editing Security Profile in host settings.

7 Select what to do with the host’s virtual machines and resource pools.

Put this host’s virtual machines in the cluster’s root resource pool

Create a resource pool for this host’s virtual machines and resource pools

8 Review settings and click Finish.

The host is added to the cluster.

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Adding Virtual Machines to a Cluster

You can add a virtual machine to a cluster in a number of ways.

When you add a host to a cluster, all virtual machines on that host are added to the cluster.

When a virtual machine is created, the New Virtual Machine wizard prompts you for the location to

place the virtual machine. You can select a standalone host or a cluster and you can select any resource pool inside the host or cluster.

You can migrate a virtual machine from a standalone host to a cluster or from a cluster to another

cluster using the Migrate Virtual Machine wizard. To start this wizard, right-click the virtual machine name and select Migrate.

Move a Virtual Machine to a Cluster

You can move a virtual machine to a cluster.

Procedure

1 Find the virtual machine in the vSphere Web Client inventory.

a To find a virtual machine, select a data center, folder, cluster, resource pool, or host.

Chapter 11 Using DRS Clusters to Manage Resources

b Click the Related Objects tab and click Virtual Machines.

2 Right-click on the virtual machine and select Move To.

3 Select a cluster.

4 Click OK.

Removing Virtual Machines from a Cluster

You can remove virtual machines from a cluster.

You can remove a virtual machine from a cluster in two ways.

When you remove a host from a cluster, all of the powered-off virtual machines that you do not migrate

to other hosts are removed as well. You can remove a host only if it is in maintenance mode or disconnected. If you remove a host from a DRS cluster, the cluster can become yellow because it is overcommitted.

You can migrate a virtual machine from a cluster to a standalone host or from a cluster to another

cluster using the Migrate Virtual Machine wizard. To start this wizard right-click the virtual machine name and select Migrate.

Move a Virtual Machine Out of a Cluster

You can move a virtual machine out of a cluster.

Procedure

1 Find the virtual machine in the vSphere Web Client inventory.

a To find a virtual machine, select a data center, folder, cluster, resource pool, or host.

b Click the Related Objects tab and click Virtual Machines.

2 Right-click the virtual machine and select Migrate.

3 Select Change datastore and click Next.

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vSphere Resource Management

4 Select a datastore and click Next.

5 Click Finish.

If the virtual machine is a member of a DRS cluster rules group, vCenter Server displays a warning before it allows the migration to proceed. The warning indicates that dependent virtual machines are not migrated automatically. You have to acknowledge the warning before migration can proceed.

Removing a Host from a Cluster

When you remove a host from a DRS cluster, you affect resource pool hierarchies, virtual machines, and you might create invalid clusters. Consider the affected objects before you remove the host.

Resource Pool Hierarchies – When you remove a host from a cluster, the host retains only the root

resource pool, even if you used a DRS cluster and decided to graft the host resource pool when you added the host to the cluster. In that case, the hierarchy remains with the cluster. You can create a hostspecific resource pool hierarchy.

NOTE Ensure that you remove the host from the cluster by first placing it in maintenance mode. If you instead disconnect the host before removing it from the cluster, the host retains the resource pool that reflects the cluster hierarchy.

Virtual Machines – A host must be in maintenance mode before you can remove it from the cluster and

for a host to enter maintenance mode all powered-on virtual machines must be migrated off that host. When you request that a host enter maintenance mode, you are also asked whether you want to migrate all the powered-off virtual machines on that host to other hosts in the cluster.

Invalid Clusters – When you remove a host from a cluster, the resources available for the cluster

decrease. If the cluster has enough resources to satisfy the reservations of all virtual machines and resource pools in the cluster, the cluster adjusts resource allocation to reflect the reduced amount of resources. If the cluster does not have enough resources to satisfy the reservations of all resource pools, but there are enough resources to satisfy the reservations for all virtual machines, an alarm is issued and the cluster is marked yellow. DRS continues to run.

Place a Host in Maintenance Mode

You place a host in maintenance mode when you need to service it, for example, to install more memory. A host enters or leaves maintenance mode only as the result of a user request.

Virtual machines that are running on a host entering maintenance mode need to be migrated to another host (either manually or automatically by DRS) or shut down. The host is in a state of Entering Maintenance Mode until all running virtual machines are powered down or migrated to different hosts. You cannot power on virtual machines or migrate virtual machines to a host entering maintenance mode.

When no more running virtual machines are on the host, the host’s icon changes to include under maintenance and the host’s Summary panel indicates the new state. While in maintenance mode, the host does not allow you to deploy or power on a virtual machine.

NOTE DRS does not recommend (or perform, in fully automated mode) any virtual machine migrations off of a host entering maintenance or standby mode if the vSphere HA failover level would be violated after the host enters the requested mode.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Right-click the host and select Enter Maintenance Mode.

If the host is part of a partially automated or manual DRS cluster, a list of migration

recommendations for virtual machines running on the host appears.

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Chapter 11 Using DRS Clusters to Manage Resources

If the host is part of an automated DRS cluster, virtual machines are migrated to different hosts

when the host enters maintenance mode.

3 If applicable, click Yes.

The host is in maintenance mode until you select Exit Maintenance Mode.

Remove a Host from a Cluster

You can remove hosts from a cluster.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Right-click the host and select Enter Maintenance Mode.

When the host is in maintenance mode, move it to a different inventory location, either the top-level data center or to a different cluster.

3 Right-click the host and select Move To.

4 Select a new location for the lost and click OK.

When you move the host, its resources are removed from the cluster. If you grafted the host’s resource pool hierarchy onto the cluster, that hierarchy remains with the cluster.

What to do next

After you remove a host from a cluster, you can perform the following tasks.

Remove the host from vCenter Server.

Run the host as a standalone host under vCenter Server.

Move the host into another cluster.

Using Standby Mode

When a host machine is placed in standby mode, it is powered off.

Normally, hosts are placed in standby mode by the vSphere DPM feature to optimize power usage. You can also place a host in standby mode manually. However, DRS might undo (or recommend undoing) your change the next time it runs. To force a host to remain off, place it in maintenance mode and power it off.

DRS Cluster Validity

The vSphere Web Client indicates whether a DRS cluster is valid, overcommitted (yellow), or invalid (red).

DRS clusters become overcommitted or invalid for several reasons.

A cluster might become overcommitted if a host fails.

A cluster becomes invalid if vCenter Server is unavailable and you power on virtual machines using the

vSphere Web Client.

A cluster becomes invalid if the user reduces the reservation on a parent resource pool while a virtual

machine is in the process of failing over.

If changes are made to hosts or virtual machines using the vSphere Web Client while vCenter Server is

unavailable, those changes take effect. When vCenter Server becomes available again, you might find that clusters have turned red or yellow because cluster requirements are no longer met.

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cluster

Total Capacity: 12G

Reserved Capacity: 11G

Available Capacity: 1G

RP1

Reservation: 4G

Reservation Used: 4G

Unreserved: 0G

RP2

Reservation: 4G

Reservation Used: 3G

Unreserved: 1G

RP3

Reservation: 3G

Reservation Used: 3G

Unreserved: 0G

VM1, 2G

VM7, 2G

VM2, 2G

VM4, 1G VM8, 2G

VM3, 3G VM5, 2GVM6, 2G

vSphere Resource Management

When considering cluster validity scenarios, you should understand these terms.

Reservation

Reservation Used

A fixed, guaranteed allocation for the resource pool input by the user.

The sum of the reservation or reservation used (whichever is larger) for each child resource pool, added recursively.

Unreserved

This nonnegative number differs according to resource pool type.

Nonexpandable resource pools: Reservation minus reservation used.

Expandable resource pools: (Reservation minus reservation used) plus

any unreserved resources that can be borrowed from its ancestor resource pools.

Valid DRS Clusters

A valid cluster has enough resources to meet all reservations and to support all running virtual machines.

The following figure shows an example of a valid cluster with fixed resource pools and how its CPU and memory resources are computed.

Figure 11‑1. Valid Cluster with Fixed Resource Pools

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The cluster has the following characteristics:

A cluster with total resources of 12GHz.

Three resource pools, each of type Fixed (Expandable Reservation is not selected).

The total reservation of the three resource pools combined is 11GHz (4+4+3 GHz). The total is shown in

the Reserved Capacity field for the cluster.

RP1 was created with a reservation of 4GHz. Two virtual machines. (VM1 and VM7) of 2GHz each are

powered on (Reservation Used: 4GHz). No resources are left for powering on additional virtual machines. VM6 is shown as not powered on. It consumes none of the reservation.

cluster

Total Capacity: 16G

Reserved Capacity: 16G

Available Capacity: 0G

RP1 (expandable)

Reservation: 4G

Reservation Used: 6G

Unreserved: 0G

RP2

Reservation: 5G

Reservation Used: 3G

Unreserved: 2G

RP3 (expandable)

Reservation: 5G

Reservation Used: 5G

Unreserved: 0G

VM1, 2G

VM7, 2G

VM2, 2G

VM4, 1G VM8, 2G

VM3, 3G VM5, 2GVM6, 2G

Chapter 11 Using DRS Clusters to Manage Resources

RP2 was created with a reservation of 4GHz. Two virtual machines of 1GHz and 2GHz are powered on

(Reservation Used: 3GHz). 1GHz remains unreserved.

RP3 was created with a reservation of 3GHz. One virtual machine with 3GHz is powered on. No

resources for powering on additional virtual machines are available.

The following figure shows an example of a valid cluster with some resource pools (RP1 and RP3) using reservation type Expandable.

Figure 11‑2. Valid Cluster with Expandable Resource Pools

A valid cluster can be configured as follows:

A cluster with total resources of 16GHz.

RP1 and RP3 are of type Expandable, RP2 is of type Fixed.

The total reservation used of the three resource pools combined is 16GHz (6GHz for RP1, 5GHz for

RP2, and 5GHz for RP3). 16GHz shows up as the Reserved Capacity for the cluster at top level.

RP1 was created with a reservation of 4GHz. Three virtual machines of 2GHz each are powered on.

Two of those virtual machines (for example, VM1 and VM7) can use RP1’s reservations, the third virtual machine (VM6) can use reservations from the cluster’s resource pool. (If the type of this resource pool were Fixed, you could not power on the additional virtual machine.)

RP2 was created with a reservation of 5GHz. Two virtual machines of 1GHz and 2GHz are powered on

(Reservation Used: 3GHz). 2GHz remains unreserved.

RP3 was created with a reservation of 5GHz. Two virtual machines of 3GHz and 2GHz are powered on. Even though this resource pool is of type Expandable, no additional 2GHz virtual machine can be powered on because the parent’s extra resources are already used by RP1.

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cluster

Total Capacity: 12G 8G

Reserved Capacity: 12G

Available Capacity: 0G

RP1 (expandable)

Reservation: 4G

Reservation Used: 4G

Unreserved: 0G

RP2

Reservation: 5G

Reservation Used: 3G

Unreserved: 2G

RP3 (expandable)

Reservation: 3G

Reservation Used: 3G

Unreserved: 0G

VM1, 2G

VM7, 0G

VM2, 2G

VM4, 1G

VM3, 3G VM5, 5GVM6, 2G

vSphere Resource Management

Overcommitted DRS Clusters

A cluster becomes overcommitted (yellow) when the tree of resource pools and virtual machines is internally consistent but the cluster does not have the capacity to support all resources reserved by the child resource pools.

There will always be enough resources to support all running virtual machines because, when a host becomes unavailable, all its virtual machines become unavailable. A cluster typically turns yellow when cluster capacity is suddenly reduced, for example, when a host in the cluster becomes unavailable. VMware recommends that you leave adequate additional cluster resources to avoid your cluster turning yellow.

Figure 11‑3. Yellow Cluster

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In this example:

A cluster with total resources of 12GHz coming from three hosts of 4GHz each.

Three resource pools reserving a total of 12GHz.

The total reservation used by the three resource pools combined is 12GHz (4+5+3 GHz). That shows up

as the Reserved Capacity in the cluster.

One of the 4GHz hosts becomes unavailable, so total resources reduce to 8GHz.

At the same time, VM4 (1GHz) and VM3 (3GHz), which were running on the host that failed, are no

longer running.

The cluster is now running virtual machines that require a total of 6GHz. The cluster still has 8GHz

available, which is sufficient to meet virtual machine requirements.

The resource pool reservations of 12GHz can no longer be met, so the cluster is marked as yellow.

cluster

Total Capacity: 12G

Reserved Capacity: 12G 15G

Available Capacity: 0G

RP1 (expandable)

Reservation: 4G

Reservation Used: 4G

Unreserved: 0G

RP2

Reservation: 2G

Reservation Used: 2G 5G

Unreserved: 0G

RP3 (expandable)

Reservation: 6G

Reservation Used: 2G

Unreserved: 4G 0G

VM1, 1G

VM7, 3G

VM2, 3G VM3, 1G VM4, 1G VM5, 1G VM6, 1G

Chapter 11 Using DRS Clusters to Manage Resources

Invalid DRS Clusters

A cluster enabled for DRS becomes invalid (red) when the tree is no longer internally consistent, that is, resource constraints are not observed.

The total amount of resources in the cluster does not affect whether the cluster is red. A cluster can be red, even if enough resources exist at the root level, if there is an inconsistency at a child level.

You can resolve a red DRS cluster problem either by powering off one or more virtual machines, moving virtual machines to parts of the tree that have sufficient resources, or editing the resource pool settings in the red part. Adding resources typically helps only when you are in the yellow state.

A cluster can also turn red if you reconfigure a resource pool while a virtual machine is failing over. A virtual machine that is failing over is disconnected and does not count toward the reservation used by the parent resource pool. You might reduce the reservation of the parent resource pool before the failover completes. After the failover is complete, the virtual machine resources are again charged to the parent resource pool. If the pool’s usage becomes larger than the new reservation, the cluster turns red.

If a user is able to start a virtual machine (in an unsupported way) with a reservation of 3GHz under resource pool 2, the cluster would become red, as shown in the following figure.

Figure 11‑4. Red Cluster

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Managing Power Resources

The vSphere Distributed Power Management (DPM) feature allows a DRS cluster to reduce its power consumption by powering hosts on and off based on cluster resource utilization.

vSphere DPM monitors the cumulative demand of all virtual machines in the cluster for memory and CPU resources and compares this to the total available resource capacity of all hosts in the cluster. If sufficient excess capacity is found, vSphere DPM places one or more hosts in standby mode and powers them off after migrating their virtual machines to other hosts. Conversely, when capacity is deemed to be inadequate, DRS brings hosts out of standby mode (powers them on) and uses vMotion to migrate virtual machines to them. When making these calculations, vSphere DPM considers not only current demand, but it also honors any user-specified virtual machine resource reservations.

NOTE ESXi hosts cannot automatically be brought out of standby mode unless they are running in a cluster managed by vCenter Server.

vSphere DPM can use one of three power management protocols to bring a host out of standby mode: Intelligent Platform Management Interface (IPMI), Hewlett-Packard Integrated Lights-Out (iLO), or WakeOn-LAN (WOL). Each protocol requires its own hardware support and configuration. If a host does not support any of these protocols it cannot be put into standby mode by vSphere DPM. If a host supports multiple protocols, they are used in the following order: IPMI, iLO, WOL.

NOTE Do not disconnect a host in standby mode or move it out of the DRS cluster without first powering it on, otherwise vCenter Server is not able to power the host back on.

Configure IPMI or iLO Settings for vSphere DPM

IPMI is a hardware-level specification and Hewlett-Packard iLO is an embedded server management technology. Each of them describes and provides an interface for remotely monitoring and controlling computers.

You must perform the following procedure on each host.

Prerequisites

Both IPMI and iLO require a hardware Baseboard Management Controller (BMC) to provide a gateway for accessing hardware control functions, and allow the interface to be accessed from a remote system using serial or LAN connections. The BMC is powered-on even when the host itself is powered-off. If properly enabled, the BMC can respond to remote power-on commands.

If you plan to use IPMI or iLO as a wake protocol, you must configure the BMC. BMC configuration steps vary according to model. See your vendor’s documentation for more information. With IPMI, you must also ensure that the BMC LAN channel is configured to be always available and to allow operator-privileged commands. On some IPMI systems, when you enable "IPMI over LAN" you must configure this in the BIOS and specify a particular IPMI account.

vSphere DPM using only IPMI supports MD5- and plaintext-based authentication, but MD2-based authentication is not supported. vCenter Server uses MD5 if a host's BMC reports that it is supported and enabled for the Operator role. Otherwise, plaintext-based authentication is used if the BMC reports it is supported and enabled. If neither MD5 nor plaintext authentication is enabled, IPMI cannot be used with the host and vCenter Server attempts to use Wake-on-LAN.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under System, click Power Management.

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4 Click Edit.

5 Enter the following information.

User name and password for a BMC account. (The user name must have the ability to remotely

power the host on.)

IP address of the NIC associated with the BMC, as distinct from the IP address of the host. The IP

address should be static or a DHCP address with infinite lease.

MAC address of the NIC associated with the BMC.

6 Click OK.

Test Wake-on-LAN for vSphere DPM

The use of Wake-on-LAN (WOL) for the vSphere DPM feature is fully supported, if you configure and successfully test it according to the VMware guidelines. You must perform these steps before enabling vSphere DPM for a cluster for the first time or on any host that is being added to a cluster that is using vSphere DPM.

Prerequisites

Before testing WOL, ensure that your cluster meets the prerequisites.

Your cluster must contain at least two hosts that are version ESX 3.5 (or ESX 3i version 3.5) or later.

Each host's vMotion networking link must be working correctly. The vMotion network should also be a

single IP subnet, not multiple subnets separated by routers.

The vMotion NIC on each host must support WOL. To check for WOL support, first determine the

name of the physical network adapter corresponding to the VMkernel port by selecting the host in the inventory panel of the vSphere Web Client, selecting the Configuration tab, and clicking Networking. After you have this information, click on Network Adapters and find the entry corresponding to the network adapter. The Wake On LAN Supported column for the relevant adapter should show Yes.

To display the WOL-compatibility status for each NIC on a host, select the host in the inventory panel

of the vSphere Web Client, select the Configuration tab, and click Network Adapters. The NIC must show Yes in the Wake On LAN Supported column.

The switch port that each WOL-supporting vMotion NIC is plugged into should be set to auto negotiate

the link speed, and not set to a fixed speed (for example, 1000 Mb/s). Many NICs support WOL only if they can switch to 100 Mb/s or less when the host is powered off.

After you verify these prerequisites, test each ESXi host that is going to use WOL to support vSphere DPM. When you test these hosts, ensure that the vSphere DPM feature is disabled for the cluster.

CAUTION Ensure that any host being added to a vSphere DPM cluster that uses WOL as a wake protocol is tested and disabled from using power management if it fails the testing. If this is not done, vSphere DPM might power off hosts that it subsequently cannot power back up.

Procedure

1 Browse to the host in the vSphere Web Client navigator.

2 Right-click the host and select Enter Standby Mode

This action powers down the host.

3 Right-click the host and select Power On to attempt to bring it out of standby mode.

4 Observe whether or not the host successfully powers back on.

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5 For any host that fails to exit standby mode successfully, perform the following steps.

a Select the host in the vSphere Web Client navigator and select the Manage tab.

b Under Power Management, click Edit to adjust the power management policy.

After you do this, vSphere DPM does not consider that host a candidate for being powered off.

Enabling vSphere DPM for a DRS Cluster

After you have performed configuration or testing steps required by the wake protocol you are using on each host, you can enable vSphere DPM.

Configure the power management automation level, threshold, and host-level overrides. These settings are configured under Power Management in the cluster’s Settings dialog box.

You can also create scheduled tasks to enable and disable DPM for a cluster using the Schedule Task: Change Cluster Power Settings wizard.

NOTE If a host in your DRS cluster has USB devices connected, disable DPM for that host. Otherwise, DPM might turn off the host and sever the connection between the device and the virtual machine that was using it.

Automation Level

Whether the host power state and migration recommendations generated by vSphere DPM are executed automatically or not depends upon the power management automation level selected for the feature.

The automation level is configured under Power Management in the cluster’s Settings dialog box.

NOTE The power management automation level is not the same as the DRS automation level.

Table 11‑1. Power Management Automation Level

Option Description

Off The feature is disabled and no recommendations will be made.

Manual Host power operation and related virtual machine migration recommendations are made, but

not automatically executed. These recommendations appear on the cluster’s DRS tab in the vSphere Web Client.

Automatic Host power operations are automatically executed if related virtual machine migrations can

all be executed automatically.

vSphere DPM Threshold

The power state (host power on or off) recommendations generated by the vSphere DPM feature are assigned priorities that range from priority-one recommendations to priority-five recommendations.

These priority ratings are based on the amount of over- or under-utilization found in the DRS cluster and the improvement that is expected from the intended host power state change. A priority-one recommendation is mandatory, while a priority-five recommendation brings only slight improvement.

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The threshold is configured under Power Management in the cluster’s Settings dialog box. Each level you move the vSphere DPM Threshold slider to the right allows the inclusion of one more lower level of priority in the set of recommendations that are executed automatically or appear as recommendations to be manually executed. At the Conservative setting, vSphere DPM only generates priority-one recommendations, the next level to the right only priority-two and higher, and so on, down to the Aggressive level which generates priority-five recommendations and higher (that is, all recommendations.)

NOTE The DRS threshold and the vSphere DPM threshold are essentially independent. You can differentiate the aggressiveness of the migration and host-power-state recommendations they respectively provide.

Host-Level Overrides

When you enable vSphere DPM in a DRS cluster, by default all hosts in the cluster inherit its vSphere DPM automation level.

You can override this default for an individual host by selecting the Host Options page of the cluster's Settings dialog box and clicking its Power Management setting. You can change this setting to the following options:

Disabled

Manual

Automatic

NOTE Do not change a host's Power Management setting if it has been set to Disabled due to failed exit standby mode testing.

After enabling and running vSphere DPM, you can verify that it is functioning properly by viewing each host’s Last Time Exited Standby information displayed on the Host Options page in the cluster Settings dialog box and on the Hosts tab for each cluster. This field shows a timestamp and whether vCenter Server Succeeded or Failed the last time it attempted to bring the host out of standby mode. If no such attempt has been made, the field displays Never.

NOTE Times for the Last Time Exited Standby text box are derived from the vCenter Server event log. If this log is cleared, the times are reset to Never.

Monitoring vSphere DPM

You can use event-based alarms in vCenter Server to monitor vSphere DPM.

The most serious potential error you face when using vSphere DPM is the failure of a host to exit standby mode when its capacity is needed by the DRS cluster. You can monitor for instances when this error occurs by using the preconfigured Exit Standby Error alarm in vCenter Server. If vSphere DPM cannot bring a host out of standby mode (vCenter Server event DrsExitStandbyModeFailedEvent), you can configure this alarm to send an alert email to the administrator or to send notification using an SNMP trap. By default, this alarm is cleared after vCenter Server is able to successfully connect to that host.

To monitor vSphere DPM activity, you can also create alarms for the following vCenter Server events.

Table 11‑2. vCenter Server Events

Event Type Event Name

Entering Standby mode (about to power off host)

Successfully entered Standby mode (host power off succeeded)

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DrsEnteredStandbyModeEvent

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Table 11‑2. vCenter Server Events (Continued)

Event Type Event Name

Exiting Standby mode (about to power on the host)

Successfully exited Standby mode (power on succeeded)

For more information about creating and editing alarms, see the vSphere Monitoring and Performance documentation.

If you use monitoring software other than vCenter Server, and that software triggers alarms when physical hosts are powered off unexpectedly, you might have a situation where false alarms are generated when vSphere DPM places a host into standby mode. If you do not want to receive such alarms, work with your vendor to deploy a version of the monitoring software that is integrated with vCenter Server. You could also use vCenter Server itself as your monitoring solution, because starting with vSphere 4.x, it is inherently aware of vSphere DPM and does not trigger these false alarms.

Using DRS Affinity Rules

You can control the placement of virtual machines on hosts within a cluster by using affinity rules.

You can create two types of rules.

Used to specify affinity or anti-affinity between a group of virtual machines and a group of hosts. An

affinity rule specifies that the members of a selected virtual machine DRS group can or must run on the members of a specific host DRS group. An anti-affinity rule specifies that the members of a selected virtual machine DRS group cannot run on the members of a specific host DRS group.

DrsExitingStandbyModeEvent

DrsExitedStandbyModeEvent

See “VM-Host Affinity Rules,” on page 88 for information about creating and using this type of rule.

Used to specify affinity or anti-affinity between individual virtual machines. A rule specifying affinity

causes DRS to try to keep the specified virtual machines together on the same host, for example, for performance reasons. With an anti-affinity rule, DRS tries to keep the specified virtual machines apart, for example, so that when a problem occurs with one host, you do not lose both virtual machines.

See “VM-VM Affinity Rules,” on page 87 for information about creating and using this type of rule.

When you add or edit an affinity rule, and the cluster's current state is in violation of the rule, the system continues to operate and tries to correct the violation. For manual and partially automated DRS clusters, migration recommendations based on rule fulfillment and load balancing are presented for approval. You are not required to fulfill the rules, but the corresponding recommendations remain until the rules are fulfilled.

To check whether any enabled affinity rules are being violated and cannot be corrected by DRS, select the cluster's DRS tab and click Faults. Any rule currently being violated has a corresponding fault on this page. Read the fault to determine why DRS is not able to satisfy the particular rule. Rules violations also produce a log event.

NOTE VM-VM and VM-Host affinity rules are different from an individual host’s CPU affinity rules.

Create a Host DRS Group

A VM-Host affinity rule establishes an affinity (or anti-affinity) relationship between a virtual machine DRS group with a host DRS group. You must create both of these groups before you can create a rule that links them.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab.

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3 Click Settings, and click DRS Groups.

4 In the DRS Groups section, click Add.

5 In the Create DRS Group dialog box, type a name for the group.

6 Select Host DRS Group from the Type drop down box and click Add.

7 Click the check box next to a host to add it. Continue this process until all desired hosts have been

added.

8 Click OK.

What to do next

Using this host DRS group, you can create a VM-Host affinity rule that establishes an affinity (or antiaffinity) relationship with an appropriate virtual machine DRS group.

“Create a Virtual Machine DRS Group,” on page 87

“Create a VM-Host Affinity Rule,” on page 89

Create a Virtual Machine DRS Group

Affinity rules establish an affinity (or anti-affinity) relationship between DRS groups. You must create DRS groups before you can create a rule that links them.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab.

3 Click Settings, and click DRS Groups.

4 In the DRS Groups section, click Add.

5 In the Create DRS Group dialog box, type a name for the group.

6 Select VM DRS Group from the Type drop down box and click Add.

7 Click the check box next to a virtual machine to add it. Continue this process until all desired virtual

machines have been added.

8 Click OK.

What to do next

“Create a Host DRS Group,” on page 86

“Create a VM-Host Affinity Rule,” on page 89

“Create a VM-VM Affinity Rule,” on page 88

VM-VM Affinity Rules

A VM-VM affinity rule specifies whether selected individual virtual machines should run on the same host or be kept on separate hosts. This type of rule is used to create affinity or anti-affinity between individual virtual machines that you select.

When an affinity rule is created, DRS tries to keep the specified virtual machines together on the same host. You might want to do this, for example, for performance reasons.

With an anti-affinity rule, DRS tries to keep the specified virtual machines apart. You could use such a rule if you want to guarantee that certain virtual machines are always on different physical hosts. In that case, if a problem occurs with one host, not all virtual machines would be placed at risk.

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Create a VM-VM Affinity Rule

You can create VM-VM affinity rules to specify whether selected individual virtual machines should run on the same host or be kept on separate hosts.

NOTE If you use the vSphere HA Specify Failover Hosts admission control policy and designate multiple failover hosts, VM-VM affinity rules are not supported.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab.

3 Click Settings and click DRS Rules.

4 Click Add.

5 In the Create DRS Rule dialog box, type a name for the rule.

6 From the Type drop-down menu, select either Keep Virtual Machines Together or Separate Virtual

Machines.

7 Click Add.

8 Select at least two virtual machines to which the rule will apply and click OK.

9 Click OK.

VM-VM Affinity Rule Conflicts

You can create and use multiple VM-VM affinity rules, however, this might lead to situations where the rules conflict with one another.

If two VM-VM affinity rules are in conflict, you cannot enable both. For example, if one rule keeps two virtual machines together and another rule keeps the same two virtual machines apart, you cannot enable both rules. Select one of the rules to apply and disable or remove the conflicting rule.

When two VM-VM affinity rules conflict, the older one takes precedence and the newer rule is disabled. DRS only tries to satisfy enabled rules and disabled rules are ignored. DRS gives higher precedence to preventing violations of anti-affinity rules than violations of affinity rules.

VM-Host Affinity Rules

A VM-Host affinity rule specifies whether or not the members of a selected virtual machine DRS group can run on the members of a specific host DRS group.

Unlike a VM-VM affinity rule, which specifies affinity (or anti-affinity) between individual virtual machines, a VM-Host affinity rule specifies an affinity relationship between a group of virtual machines and a group of hosts. There are 'required' rules (designated by "must") and 'preferential' rules (designated by "should".)

A VM-Host affinity rule includes the following components.

One virtual machine DRS group.

One host DRS group.

A designation of whether the rule is a requirement ("must") or a preference ("should") and whether it is

affinity ("run on") or anti-affinity ("not run on").

Because VM-Host affinity rules are cluster-based, the virtual machines and hosts that are included in a rule must all reside in the same cluster. If a virtual machine is removed from the cluster, it loses its DRS group affiliation, even if it is later returned to the cluster.

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Create a VM-Host Affinity Rule

You can create VM-Host affinity rules to specify whether or not the members of a selected virtual machine DRS group can run on the members of a specific host DRS group.

Prerequisites

Create the virtual machine and host DRS groups to which the VM-Host affinity rule applies.

Procedure

1 Browse to the cluster in the vSphere Web Client navigator.

2 Click the Manage tab.

3 Click Settings and click DRS Rules.

4 Click Add.

5 In the Create DRS Rule dialog box, type a name for the rule.

6 From the Type drop down menu, select Virtual Machines to Hosts.

7 Select the virtual machine DRS group and the host DRS group to which the rule applies.

8 Select a specification for the rule.

Must run on hosts in group. Virtual machines in VM Group 1 must run on hosts in Host Group A.

Should run on hosts in group. Virtual machines in VM Group 1 should, but are not required, to

run on hosts in Host Group A.

Must not run on hosts in group. Virtual machines in VM Group 1 must never run on host in Host

Group A.

Should not run on hosts in group. Virtual machines in VM Group 1 should not, but might, run on

hosts in Host Group A.

9 Click OK.

Using VM-Host Affinity Rules

You use a VM-Host affinity rule to specify an affinity relationship between a group of virtual machines and a group of hosts. When using VM-Host affinity rules, you should be aware of when they could be most useful, how conflicts between rules are resolved, and the importance of caution when setting required affinity rules.

One use case where VM-Host affinity rules are helpful is when the software you are running in your virtual machines has licensing restrictions. You can place such virtual machines into a DRS group and then create a rule that requires them to run on a host DRS group that contains only host machines that have the required licenses.

NOTE When you create a VM-Host affinity rule that is based on the licensing or hardware requirements of the software running in your virtual machines, you are responsible for ensuring that the groups are properly set up. The rule does not monitor the software running in the virtual machines nor does it know what non-VMware licenses are in place on which ESXi hosts.

If you create more than one VM-Host affinity rule, the rules are not ranked, but are applied equally. Be aware that this has implications for how the rules interact. For example, a virtual machine that belongs to two DRS groups, each of which belongs to a different required rule, can run only on hosts that belong to both of the host DRS groups represented in the rules.

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When you create a VM-Host affinity rule, its ability to function in relation to other rules is not checked. So it is possible for you to create a rule that conflicts with the other rules you are using. When two VM-Host affinity rules conflict, the older one takes precedence and the newer rule is disabled. DRS only tries to satisfy enabled rules and disabled rules are ignored.

DRS, vSphere HA, and vSphere DPM never take any action that results in the violation of required affinity rules (those where the virtual machine DRS group 'must run on' or 'must not run on' the host DRS group). Accordingly, you should exercise caution when using this type of rule because of its potential to adversely affect the functioning of the cluster. If improperly used, required VM-Host affinity rules can fragment the cluster and inhibit the proper functioning of DRS, vSphere HA, and vSphere DPM.

A number of cluster functions are not performed if doing so would violate a required affinity rule.

DRS does not evacuate virtual machines to place a host in maintenance mode.

DRS does not place virtual machines for power-on or load balance virtual machines.

vSphere HA does not perform failovers.

vSphere DPM does not optimize power management by placing hosts into standby mode.

To avoid these situations, exercise caution when creating more than one required affinity rule or consider using VM-Host affinity rules that are preferential only (those where the virtual machine DRS group 'should run on' or 'should not run on' the host DRS group). Ensure that the number of hosts in the cluster with which each virtual machine is affined is large enough that losing a host does not result in a lack of hosts on which the virtual machine can run. Preferential rules can be violated to allow the proper functioning of DRS, vSphere HA, and vSphere DPM.

NOTE You can create an event-based alarm that is triggered when a virtual machine violates a VM-Host affinity rule. In the vSphere Web Client, add a new alarm for the virtual machine and select VM is violating VM-Host Affinity Rule as the event trigger. For more information about creating and editing alarms, see the vSphere Monitoring and Performance documentation.

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Creating a Datastore Cluster 12

A datastore cluster is a collection of datastores with shared resources and a shared management interface. Datastore clusters are to datastores what clusters are to hosts. When you create a datastore cluster, you can use vSphere Storage DRS to manage storage resources.

NOTE Datastore clusters are referred to as storage pods in the vSphere API.

When you add a datastore to a datastore cluster, the datastore's resources become part of the datastore cluster's resources. As with clusters of hosts, you use datastore clusters to aggregate storage resources, which enables you to support resource allocation policies at the datastore cluster level. The following resource management capabilities are also available per datastore cluster.

Space utilization load balancing

You can set a threshold for space use. When space use on a datastore exceeds the threshold, Storage DRS generates recommendations or performs Storage vMotion migrations to balance space use across the datastore cluster.

I/O latency load balancing

You can set an I/O latency threshold for bottleneck avoidance. When I/O latency on a datastore exceeds the threshold, Storage DRS generates recommendations or performs Storage vMotion migrations to help alleviate high I/O load.

Anti-affinity rules

You can create anti-affinity rules for virtual machine disks. For example, the virtual disks of a certain virtual machine must be kept on different datastores. By default, all virtual disks for a virtual machine are placed on the same datastore.

This chapter includes the following topics:

“Initial Placement and Ongoing Balancing,” on page 92

“Storage Migration Recommendations,” on page 92

“Create a Datastore Cluster,” on page 92

“Enable and Disable Storage DRS,” on page 93

“Set the Automation Level for Datastore Clusters,” on page 93

“Setting the Aggressiveness Level for Storage DRS,” on page 94

“Datastore Cluster Requirements,” on page 95

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Initial Placement and Ongoing Balancing

Storage DRS provides initial placement and ongoing balancing recommendations to datastores in a Storage DRS-enabled datastore cluster.

Initial placement occurs when Storage DRS selects a datastore within a datastore cluster on which to place a virtual machine disk. This happens when the virtual machine is being created or cloned, when a virtual machine disk is being migrated to another datastore cluster, or when you add a disk to an existing virtual machine.

Initial placement recommendations are made in accordance with space constraints and with respect to the goals of space and I/O load balancing. These goals aim to minimize the risk of over-provisioning one datastore, storage I/O bottlenecks, and performance impact on virtual machines.

Storage DRS is invoked at the configured frequency (by default, every eight hours) or when one or more datastores in a datastore cluster exceeds the user-configurable space utilization thresholds. When Storage DRS is invoked, it checks each datastore's space utilization and I/O latency values against the threshold. For I/O latency, Storage DRS uses the 90th percentile I/O latency measured over the course of a day to compare against the threshold.

Storage Migration Recommendations

vCenter Server displays migration recommendations on the Storage DRS Recommendations page for datastore clusters that have manual automation mode.

The system provides as many recommendations as necessary to enforce Storage DRS rules and to balance the space and I/O resources of the datastore cluster. Each recommendation includes the virtual machine name, the virtual disk name, the name of the datastore cluster, the source datastore, the destination datastore, and a reason for the recommendation.

Balance datastore space use

Balance datastore I/O load

Storage DRS makes mandatory recommendations for migration in the following situations:

The datastore is out of space.

Anti-affinity or affinity rules are being violated.

The datastore is entering maintenance mode and must be evacuated.

In addition, optional recommendations are made when a datastore is close to running out of space or when adjustments should be made for space and I/O load balancing.

Storage DRS considers moving virtual machines that are powered off or powered on for space balancing. Storage DRS includes powered-off virtual machines with snapshots in these considerations.

Create a Datastore Cluster

You can manage datastore cluster resources using Storage DRS.

Procedure

1 Browse to Datacenters in the vSphere Web Client navigator.

2 Right-click the datacenter object and select New Datastore Cluster.

3 Follow the prompts to complete the New Datastore Cluster wizard.

4 Click Finish.

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Enable and Disable Storage DRS

Storage DRS allows you to manage the aggregated resources of a datastore cluster. When Storage DRS is enabled, it provides recommendations for virtual machine disk placement and migration to balance space and I/O resources across the datastores in the datastore cluster.

When you enable Storage DRS, you enable the following functions.

Space load balancing among datastores within a datastore cluster.

I/O load balancing among datastores within a datastore cluster.

Initial placement for virtual disks based on space and I/O workload.

The Enable Storage DRS check box in the Datastore Cluster Settings dialog box enables or disables all of these components at once. If necessary, you can disable I/O-related functions of Storage DRS independently of space balancing functions.

When you disable Storage DRS on a datastore cluster, Storage DRS settings are preserved. When you enable Storage DRS, the settings for the datastore cluster are restored to the point where Storage DRS was disabled.

Procedure

1 Browse to the datastore cluster in the vSphere Web Client navigator.

Chapter 12 Creating a Datastore Cluster

2 Click the Manage tab and click Settings.

3 Under Services, select Storage DRS and click Edit.

4 Select Turn ON vSphere DRS and click OK.

5 (Optional) To disable only I/O-related functions of Storage DRS, leaving space-related controls enabled,

perform the following steps.

a Under Storage DRS select Edit.

b Deselect the Enable I/O metric for Storage DRS check box and click OK.

Set the Automation Level for Datastore Clusters

The automation level for a datastore cluster specifies whether or not placement and migration recommendations from Storage DRS are applied automatically.

Procedure

1 Browse to the datastore cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Services, select DRS and click Edit.

4 Expand DRS Automation and select an automation level.

Manual is the default automation level.

Option Description

No Automation (Manual Mode)

Partially Automated

Fully Automated

Placement and migration recommendations are displayed, but do not run until you manually apply the recommendation.

Placement recommendations run automatically and migration recommendations are displayed, but do not run until you manually apply the recommendation.

Placement and migration recommendations run automatically.

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5 Click OK.

Setting the Aggressiveness Level for Storage DRS

The aggressiveness of Storage DRS is determined by specifying thresholds for space used and I/O latency.

Storage DRS collects resource usage information for the datastores in a datastore cluster. vCenter Server uses this information to generate recommendations for placement of virtual disks on datastores.

When you set a low aggressiveness level for a datastore cluster, Storage DRS recommends Storage vMotion migrations only when absolutely necessary, for example, if when I/O load, space utilization, or their imbalance is high. When you set a high aggressiveness level for a datastore cluster, Storage DRS recommends migrations whenever the datastore cluster can benefit from space or I/O load balancing.

In the vSphere Web Client, you can use the following thresholds to set the aggressiveness level for Storage DRS:

Space Utilization

I/O Latency

You can also set advanced options to further configure the aggressiveness level of Storage DRS.

Space utilization difference

I/O load balancing invocation interval

I/O imbalance threshold

Storage DRS generates recommendations or performs migrations when the percentage of space utilization on the datastore is greater than the threshold you set in the vSphere Web Client.

Storage DRS generates recommendations or performs migrations when the 90th percentile I/O latency measured over a day for the datastore is greater than the threshold.

This threshold ensures that there is some minimum difference between the space utilization of the source and the destination. For example, if the space used on datastore A is 82% and datastore B is 79%, the difference is 3. If the threshold is 5, Storage DRS will not make migration recommendations from datastore A to datastore B.

After this interval, Storage DRS runs to balance I/O load.

Lowering this value makes I/O load balancing less aggressive. Storage DRS computes an I/O fairness metric between 0 and 1, which 1 being the fairest distribution. I/O load balancing runs only if the computed metric is less than 1 - (I/O imbalance threshold / 100).

Set Storage DRS Runtime Rules

Set Storage DRS triggers and configure advanced options for the datastore cluster.

Procedure

1 (Optional) Select or deselect the Enable I/O metric for SDRS recommendations check box to enable or

disable I/O metric inclusion.

When you disable this option, vCenter Server does not consider I/O metrics when making Storage DRS recommendations. When you disable this option, you disable the following elements of Storage DRS:

I/O load balancing among datastores within a datastore cluster.

Initial placement for virtual disks based on I/O workload. Initial placement is based on space only.

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2 (Optional) Set Storage DRS thresholds.

You set the aggressiveness level of Storage DRS by specifying thresholds for used space and I/O latency.

Use the Utilized Space slider to indicate the maximum percentage of consumed space allowed

before Storage DRS is triggered. Storage DRS makes recommendations and performs migrations when space use on the datastores is higher than the threshold.

Use the I/O Latency slider to indicate the maximum I/O latency allowed before Storage DRS is

triggered. Storage DRS makes recommendations and performs migrations when latency is higher than the threshold.

NOTE The Storage DRS I/O Latency threshold for the datastore cluster should be lower than or equal to the Storage I/O Control congestion threshold.

3 (Optional) Configure advanced options.

No recommendations until utilization difference between source and destination is: Use the slider

to specify the space utilization difference threshold. Utilization is usage * 100/capacity.

Check imbalances every: Specify how often Storage DRS should assess space and I/O load

balancing.

I/O imbalance threshold: Use the slider to indicate the aggressiveness of I/O load balancing.

4 Click OK.

Datastore Cluster Requirements

Datastores and hosts that are associated with a datastore cluster must meet certain requirements to use datastore cluster features successfully.

Follow these guidelines when you create a datastore cluster.

Datastore clusters must contain similar or interchangeable datastores.

A datastore cluster can contain a mix of datastores with different sizes and I/O capacities, and can be from different arrays and vendors. However, the following types of datastores cannot coexist in a datastore cluster.

NFS and VMFS datastores cannot be combined in the same datastore cluster.

Replicated datastores cannot be combined with non-replicated datastores in the same Storage-DRS-

enabled datastore cluster.

All hosts attached to the datastores in a datastore cluster must be ESXi 5.0 and later. If datastores in the

datastore cluster are connected to ESX/ESXi 4.x and earlier hosts, Storage DRS does not run.

Datastores shared across multiple data centers cannot be included in a datastore cluster.

As a best practice, do not include datastores that have hardware acceleration enabled in the same

datastore cluster as datastores that do not have hardware acceleration enabled. Datastores in a datastore cluster must be homogeneous to guarantee hardware acceleration-supported behavior.

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Adding and Removing Datastores from a Datastore Cluster

You add and remove datastores to and from an existing datastore cluster.

You can add to a datastore cluster any datastore that is mounted on a host in the vSphere Web Client inventory, with the following exceptions:

All hosts attached to the datastore must be ESXi 5.0 and later.

The datastore cannot be in more than one data center in the same instance of the vSphere Web Client.

When you remove a datastore from a datastore cluster, the datastore remains in the vSphere Web Client inventory and is not unmounted from the host.

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Using Datastore Clusters to Manage

Storage Resources 13

After you create a datastore cluster, you can customize it and use it to manage storage I/O and space utilization resources.

This chapter includes the following topics:

“Using Storage DRS Maintenance Mode,” on page 97

“Applying Storage DRS Recommendations,” on page 99

“Change Storage DRS Automation Level for a Virtual Machine,” on page 100

“Set Up Off-Hours Scheduling for Storage DRS,” on page 100

“Storage DRS Anti-Affinity Rules,” on page 101

“Clear Storage DRS Statistics,” on page 104

“Storage vMotion Compatibility with Datastore Clusters,” on page 105

Using Storage DRS Maintenance Mode

You place a datastore in maintenance mode when you need to take it out of use to service it. A datastore enters or leaves maintenance mode only as the result of a user request.

Maintenance mode is available to datastores within a Storage DRS-enabled datastore cluster. Standalone datastores cannot be placed in maintenance mode.

Virtual disks that are located on a datastore that is entering maintenance mode must be migrated to another datastore, either manually or using Storage DRS. When you attempt to put a datastore in maintenance mode, the Placement Recommendations tab displays a list of migration recommendations, datastores within the same datastore cluster where virtual disks can be migrated. On the Faults tab, vCenter Server displays a list of the disks that cannot be migrated and the reasons why. If Storage DRS affinity or antiaffinity rules prevent disks from being migrated, you can choose to enable the Ignore Affinity Rules for Maintenance option.

The datastore is in a state of Entering Maintenance Mode until all virtual disks have been migrated.

Place a Datastore in Maintenance Mode

If you need to take a datastore out of service, you can place the datastore in Storage DRS maintenance mode.

Prerequisites

Storage DRS is enabled on the datastore cluster that contains the datastore that is entering maintenance mode.

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No CD-ROM image files are stored on the datastore.

There are at least two datastores in the datastore cluster.

Procedure

1 Browse to the datastore in the vSphere Web Client navigator.

2 Right-click the datastore and select Enter Storage DRS Maintenance Mode.

A list of recommendations appears for datastore maintenance mode migration.

3 (Optional) On the Placement Recommendations tab, deselect any recommendations you do not want to

apply.

NOTE The datastore cannot enter maintenance mode without evacuating all disks. If you deselect recommendations, you must manually move the affected virtual machines.

4 If necessary, click Apply Recommendations.

vCenter Server uses Storage vMotion to migrate the virtual disks from the source datastore to the destination datastore and the datastore enters maintenance mode.

The datastore icon might not be immediately updated to reflect the datastore's current state. To update the icon immediately, click Refresh.

Ignore Storage DRS Affinity Rules for Maintenance Mode

Storage DRS affinity or anti-affinity rules might prevent a datastore from entering maintenance mode. You can ignore these rules when you put a datastore in maintenance mode.

When you enable the Ignore Affinity Rules for Maintenance option for a datastore cluster, vCenter Server ignores Storage DRS affinity and anti-affinity rules that prevent a datastore from entering maintenance mode.

Storage DRS rules are ignored only for evacuation recommendations. vCenter Server does not violate the rules when making space and load balancing recommendations or initial placement recommendations.

Procedure

1 Browse to the datastore cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under Services, select DRS and click Edit.

4 Expand Advanced Options and click Add.

5 In the Option column, type IgnoreAffinityRulesForMaintenance.

6 In the Value column, type 1 to enable the option.

Type 0 to disable the option.

7 Click OK.

The Ignore Affinity Rules for Maintenance Mode option is applied to the datastore cluster.

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Applying Storage DRS Recommendations

Storage DRS collects resource usage information for all datastores in a datastore cluster. Storage DRS uses the information to generate recommendations for virtual machine disk placement on datastores in a datastore cluster.

Storage DRS recommendations appear on the Storage DRS tab in the vSphere Web Client datastore view. Recommendations also appear when you attempt to put a datastore into Storage DRS maintenance mode. When you apply Storage DRS recommendations, vCenter Server uses Storage vMotion to migrate virtual machine disks to other datastores in the datastore cluster to balance the resources.

You can apply a subset of the recommendations by selecting the Override Suggested DRS Recommendations check box and selecting each recommendation to apply.

Table 13‑1. Storage DRS Recommendations

Label Description

Priority Priority level (1-5) of the recommendation. (Hidden by

default.)

Recommendation Action being recommended by Storage DRS.

Reason Why the action is needed.

Space Utilization % Before (source) and (destination) Percentage of space used on the source and destination

datastores before migration.

Space Utilization % After (source) and (destination) Percentage of space used on the source and destination

datastores after migration.

I/O Latency Before (source) Value of I/O latency on the source datastore before

migration.

I/O Latency Before (destination) Value of I/O latency on the destination datastore before

migration.

Refresh Storage DRS Recommendations

Storage DRS migration recommendations appear on the Storage DRS tab in the vSphere Web Client. You can refresh these recommendations by running Storage DRS.

Prerequisites

At least one datastore cluster must exist in the vSphere Web Client inventory.

Enable Storage DRS for the datastore cluster. The Storage DRS tab appears only if Storage DRS is enabled.

Procedure

1 In the vSphere Web Client datastore view, select the datastore cluster and click the Storage DRS tab.

2 Select the Recommendations view and click the Run Storage DRS link in the upper right corner.

The recommendations are updated. The Last Updated timestamp displays the time when Storage DRS recommendations were refreshed.

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Change Storage DRS Automation Level for a Virtual Machine

You can override the datastore cluster-wide automation level for individual virtual machines. You can also override default virtual disk affinity rules.

Procedure

1 Browse to the datastore cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under VM Overrides, select Add.

4 Select a virtual machine.

5 Click the Automation level drop-down menu, and select an automation level for the virtual machine.

Option Description

Default (Manual)

Fully Automated

Disabled

6 Click the Keep VMDKs together, drop-down menu to override default VMDK affinity.

Placement and migration recommendations are displayed, but do not run until you manually apply the recommendation.

Placement and migration recommendations run automatically.

vCenter Server does not migrate the virtual machine or provide migration recommendations for it.

See “Override VMDK Affinity Rules,” on page 103.

7 Click OK.

Set Up Off-Hours Scheduling for Storage DRS

You can create a scheduled task to change Storage DRS settings for a datastore cluster so that migrations for fully automated datastore clusters are more likely to occur during off-peak hours.

You can create a scheduled task to change the automation level and aggressiveness level for a datastore cluster. For example, you might configure Storage DRS to run less aggressively during peak hours, when performance is a priority, to minimize the occurrence of storage migrations. During non-peak hours, Storage DRS can run in a more aggressive mode and be invoked more frequently.

Prerequisites

Enable Storage DRS.

Procedure

1 Browse to the datastore cluster in the vSphere Web Client navigator.

2 Click the Manage tab and click Settings.

3 Under DRS click the Schedule DRS button.

4 In the Edit Datastore Cluster dialog box, click SDRS Scheduling.

100 VMware, Inc.

VMware ESXI - 6.0.1 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Contents

About vSphere Resource Management

Updated Information

Resource Types

Resource Providers

Resource Consumers

Goals of Resource Management

Resource Allocation Shares

Resource Allocation Reservation

Resource Allocation Limit

Resource Allocation Settings Suggestions

Edit Resource Settings

Changing Resource Allocation Settings—Example

Admission Control

CPU Virtualization Basics 3

Software-Based CPU Virtualization

Hardware-Assisted CPU Virtualization

Virtualization and Processor-Specific Behavior

Performance Implications of CPU Virtualization

Administering CPU Resources 4

View Processor Information

Specifying CPU Configuration

Multicore Processors

Hyperthreading

Hyperthreading and ESXi Hosts

Enable Hyperthreading

Using CPU Affinity

Assign a Virtual Machine to a Specific Processor

Potential Issues with CPU Affinity

Host Power Management Policies

Select a CPU Power Management Policy

Configure Custom Policy Parameters for Host Power Management

Memory Virtualization Basics 5

Virtual Machine Memory

Memory Overcommitment

Memory Sharing

Types of Memory Virtualization

Software-Based Memory Virtualization

Hardware-Assisted Memory Virtualization

Administering Memory Resources 6

Understanding Memory Overhead

Overhead Memory on Virtual Machines

How ESXi Hosts Allocate Memory

Memory Tax for Idle Virtual Machines

VMX Swap Files

Memory Reclamation

Memory Balloon Driver

Using Swap Files

Swap File Location

Enable Host-Local Swap for a DRS Cluster

Enable Host-Local Swap for a Standalone Host

Swap Space and Memory Overcommitment

Configure Virtual Machine Swapfile Properties for the Host

Configure a Virtual Machine Swapfile Location for a Cluster

Delete Swap Files

Sharing Memory Across Virtual Machines

Memory Compression

Enable or Disable the Memory Compression Cache

Set the Maximum Size of the Memory Compression Cache

Measuring and Differentiating Types of Memory Usage

Memory Reliability

Correcting an Error Isolation Notification

About System Swap

Configure System Swap

View Graphics Information 7

Managing Storage I/O Resources 8

Storage I/O Control Requirements

Storage I/O Control Resource Shares and Limits

View Storage I/O Control Shares and Limits

Monitor Storage I/O Control Shares

Set Storage I/O Control Resource Shares and Limits

Enable Storage I/O Control

Set Storage I/O Control Threshold Value

Storage DRS Integration with Storage Profiles

Managing Resource Pools 9

Why Use Resource Pools?