Sun Microsystems Sun Enterprise Server User's Guide

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SunEnterpriseServerAlternate Pathing User’s Guide

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805-5985-10

March 1999, Revision B

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Please

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Contents

Purpose of Alternate Pathing 1 Basic Alternate Pathing Concepts 4

Physical Path 4 Meta-Disk 5 Meta-Network 6 Disk Pathgroup 7 Network Pathgroup 8

Supported Devices and Software Versions 9 Example AP Configurations 10 AP and Domains 11 Managing Copies of the Database 13 Locating Databases to Maximize RAS 14 Creating and Deleting Databases 14

▼ To Create a Copy of the AP Database 15 ▼ To Delete a Copy of the AP Database 15

Viewing Database Information 16

▼ To View Information About Database Copies 16

Viewing Pathgroup Information 16

▼ To View Uncommitted Disk Entries 17

Contents iii

▼ To View Committed Disk Entries 17 ▼ To View Uncommitted Network Entries 18 ▼ To View Committed Network Entries 18

Device Nodes for Meta-Disks 19 Automatic Switching of Meta-Disks 20 Disk Availability and Performance Trade-Offs 22 Disk Mirroring Considerations 23 Working With Disk Pathgroups and Meta-Disks 27

▼ To Create a Disk Pathgroup and Meta-Disk 27 ▼ To Switch From the Primary Path to the Alternate Path 31 ▼ To Switch Back to the Primary Path 32 ▼ To Delete Disk Pathgroups and Meta-Disks 32 ▼ To Deconfigure a Meta-Disk 34 ▼ To Reconfigure a Meta-Disk 34

Placing the Boot Disk Under AP Control 37

▼ To Place a Boot Disk under AP Control 37 ▼ To Alternately Path a Mirrored Boot Disk 39 ▼ To Remove a Mirrored Boot Disk From AP Control 40 ▼ To Remove the Boot Disk From AP Control 40

AP Boot Sequence 40 Using Single-User Mode 41 Meta-Network Interfaces 43 Working With Network Pathgroups 44

▼ To Create a Network Pathgroup and Meta-Network 44 ▼ To Switch a Network Pathgroup 48 ▼ To Delete a Network Pathgroup and Meta-Network 49 ▼ To Deconfigure a Meta-Network 49 ▼ To Reconfigure a Meta-Network 50

iv Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Alternately Pathing the Primary Network Interface 51

▼ To Create a Network Pathgroup and Meta-Network for the Primary

Network 52

▼ To Delete the Network Pathgroup and Meta-Network for the Primary

Network 53

▼ To Deconfigure the Meta-Network for the Primary Network 54 ▼ To Reconfigure the Meta-Network for the Primary Network 55

Using AP and DR Together 57 Maintaining the Correct AP State 59

Contents v

vi Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Figures

FIGURE 1-1 Alternately Pathed I/O Device 2 FIGURE 1-2 Switching Paths After an I/O Controller Failure 3 FIGURE 1-3 Switching Paths for a DR Detach Operation 4 FIGURE 1-4 Physical Path 5 FIGURE 1-5 Meta-Disk Example 6 FIGURE 1-6 Meta-Network 7 FIGURE 1-7 Disk Pathgroup 8 FIGURE 1-8 Network Pathgroup 9 FIGURE 1-9 Typical AP Configuration 10 FIGURE 1-10 AP and Disk Mirroring 11 FIGURE 3-1 System Boards and Disk Controllers 23 FIGURE 3-2 System Boards and Controllers 24 FIGURE 3-3 Mirrored Volumes Example 1 24 FIGURE 3-4 Mirrored Volumes Example 2 25 FIGURE 3-5 Mirrored Volumes Example 3 26

Figures vii

viii Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Preface

The Sun Enterprise Server Alternate Pathing User’s Guide describes the Alternate Pathing (AP) component of the Sun™ Enterprise™ server product line. Some AP features apply only to the Sun Enterprise 10000 server. These features are noted throughout this guide.

How This Book Is Organized

This guide contains the following chapters: Chapter 1 introduces AP. Chapter 2 covers the AP database operations. Chapter 3 describes meta-disks and disk pathgroups, and explains how to use them. Chapter 4 covers unattended system boot issues. Chapter 5 describes meta-networks and network pathgroups, and explains how to

use them. Chapter 6 describes how Dynamic Reconfiguration (DR) and AP work together. Appendix A provides a list of all AP commands. Appendix B provides an overview of the underlying AP architecture. Appendix C provides an overview of the underlying AP drivers.

Before You Read This Book

This manual is intended for the Sun Enterprise system administrator, who should have a working knowledge of UNIX® systems, particularly those based on the Solaris™ operating environment. If you do not have such knowledge, you should first read the Solaris User and System Administrator AnswerBook™ documentation provided with this system, and consider UNIX system administration training.

Using UNIX Commands

This document does not contain information on basic UNIX commands and procedures such as shutting down the system, booting the system, and configuring devices.

See one or more of the following for this information:

■ AnswerBook online documentation for the Solaris software environment,

particularly those dealing with Solaris system administration

■ Other software documentation that you received with your system

x Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Typographic Conventions

TABLEP-1 Typographic Conventions

Typeface orSymbol Meaning Examples

AaBbCc123 The names of commands, files,

and directories; on-screen computer output.

AaBbCc123 What you type, when

contrasted with on-screen computer output.

AaBbCc123 Book titles, new words or terms,

words to be emphasized. Command-line variable; replace with a real name or value.

Edit your .login file. Use ls -a to list all files.

% You have mail. % su

Password:

Read Chapter 6 in the User’s Guide. These are called class options. You must be root to do this. To delete a file, type rm filename.

Shell Prompts

TABLEP-2 Shell Prompts

Shell Prompt

C shell machine_name% C shell superuser machine_name# Bourne shell and Korn shell $ Bourne shell and Korn shell superuser #

Introduction to Alternate Pathing

This chapter describes the basic purpose of Alternate Pathing and provides an overview of Alternate Pathing concepts and terminology.

Purpose of Alternate Pathing

Alternate Pathing (AP) supports high availability of I/O controllers—the hardware components that reside on system boards and enable the Sun Enterprise server to communicate with I/O devices such as disks and networks. With AP, each I/O device connects to two I/O controllers.

Sun Enterprise Ser ver

I/O

I/O controller

Active path (I/O flows here)

Passive path

(no I/O)

I/O device

FIGURE 1-1 Alternately Pathed I/O Device

System board

The I/O controllers are part of two separate electrical pathways to the I/O device, known as alternate paths. AP enables you to set up and use alternate paths on the Sun Enterprise servers.

There are two purposes for AP. One purpose is to help protect against I/O controller failures. With AP, if one I/O controller fails, you can switch to the alternate controller.

2 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

I/O controller

problem

Active path

(unavailable)

Sun Enterprise Ser ver

I/O

FIGURE 1-2 Switching Paths After an I/O Controller Failure

Sun Enterprise Server

I/O

New active path

For disk controllers, this switch occurs automatically whenever a path failure is detected during normal operation. For network controllers, you must manually switch paths (using a single AP command).

The second purpose of AP is to support Dynamic Reconfiguration (DR). DR is used to logically attach and detach system boards from the operating system without having to halt and reboot. For example, with DR you can detach a board from the operating system, physically remove and service the board, and then re-insert the board and attach it to the operating system again. You can do all of this without halting the operating system or terminating any user applications.

If you want to detach a board that is connected to an I/O device, and if that I/O device is alternately pathed, you can first use AP to redirect the I/O flow to a controller on a different board. You can then use DR to detach the system board without interrupting the I/O flow. On the Sun Enterprise 10000, the switch occurs automatically during the DR operation (for both disk and network devices), assuming a viable alternate controller exists on another board. The following figure shows the relationship between AP and DR.

Chapter 1 Introduction to Alternate Pathing 3

Sun Enterprise Server

Sun Enterprise Ser ver

Active path (unavailable)

I/O

DR Detach, and hot-swap

FIGURE 1-3 Switching Paths for a DR Detach Operation

I/O

Active path

(new)

Basic Alternate Pathing Concepts

This section discusses basic AP concepts and introduces the terminology that is used throughout this chapter.

Physical Path

For the purposes of AP, an I/O device is either a disk or network. An I/O controller is the controller card for an I/O device. An I/O port is a connector on a controller card. (Often there are two ports per controller card.) A device node is a path in the devices directory that is used to specify a physical device, for example, /dev/dsk/c0t0d1s0. The term physical path refers to the electrical path from the host to a disk or network.

4 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Sun Enterprise Ser ver

I/O

System board

and I/O controllers

I/O device

Physical path

FIGURE 1-4 Physical Path

You reference a physical device by means of a device node, for example, /dev/dsk/ c0t1d1s0.

Meta-Disk

A meta-disk, as illustrated in FIGURE 1-5, is a construct that enables you to access a disk by using either of two physical paths without having to reference either path explicitly within your scripts and programs. You reference a meta-disk (in your scripts and programs) using an AP-specific device node such as /dev/ap/dsk/ mc0t1d1s0. (See “Device Nodes for Meta-Disks” on page 19 for more information.)

In the following figure, an AP-specific device node is used to perform disk I/O, regardless of which pln port (pln2 or pln9) is currently handling I/O.

Chapter 1 Introduction to Alternate Pathing 5

Sun Enterprise Server

/dev/ap/dsk/mc0t1d1s0

System boards

pln2

I/O

FIGURE 1-5 Meta-Disk Example

SSA

pln9

SPARCstorage™ Array (SSA) controllers with one or two PLN ports. (Black PLN ports are connected to the SSA.)

SSA port

Meta-Network

A meta-network, as illustrated in FIGURE 1-6, is a construct that enables you to access a network by using either of two physical paths without having to reference either path explicitly within your scripts and programs. You reference a meta-network (in your scripts and programs) using a meta-network interface name such as mle1. (See “Meta-Network Interfaces” on page 43 for more information.)

In the following figure, mle1 is used to access a meta-network, regardless of which controller (le1 or le6) is currently processing I/O for the meta-network.

6 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Sun Enterprise Ser ver

mle1

System boards and controllers

le0

le1

le2

le3

le4

le5

le6

le7

I/O

Network

FIGURE 1-6 Meta-Network

Disk Pathgroup

A disk pathgroup, as illustrated in FIGURE 1-7, consists of two physical paths leading to the same disk array. When a physical path is part of a pathgroup, it is called an alternate path. An alternate path to a disk can be uniquely identified by the pln port or sf port that the alternate path uses. Only one alternate path at a time handles disk I/O. The alternate path that is currently handling I/O is called the active alternate.

Note that whereas a meta-disk provides a means for you to access a disk (in your scripts and programs), a disk pathgroup provides a means for you to manipulate the path to that disk (when you run AP commands). For example, to perform a switch operation (that is, change the active alternate from one alternate path to another), you reference a disk pathgroup within an apconfig(1M) command.

One of the alternate paths is designated as the primary path. The primary path is initially the active alternate. Although the active alternate changes when you perform a switch operation, the primary path remains constant. You reference a disk pathgroup by specifying the pln port (for example, pln1)orsf port (for example,

sf1) that corresponds to the primary path. (For information about determining the pln or sf port name, see “Device Nodes for Meta-Disks” on page 19.)

For example, the following figure shows the results of using the apconfig(1M) command to switch the active alternate of a disk pathgroup.

Chapter 1 Introduction to Alternate Pathing 7

Sun Enterprise Ser ver

I/O

System boards and controllers

Switch

I/O

Alternate path (primary path)

Disk array

FIGURE 1-7 Disk Pathgroup

Alternate path

(active alternate)

You reference a disk pathgroup (for example, to switch from one path to another) by specifying the primary path, for example, apconfig -P pln2 -a pln9.

Network Pathgroup

A network pathgroup, as illustrated in the following figure, consists of two network controllers connected to the same physical network. The terms alternate path, active alternate, primary path, and switch have basically the same meaning as they do for disk pathgroups.

To specify a network pathgroup, reference the corresponding meta-network interface name, for example, mle1. (Meta-network interface names are described in “MetaNetwork Interfaces” on page 43.) For example, the apconfig(1M) command to switch the active alternate of a network pathgroup.

FIGURE 1-8 shows the results of using

8 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

Sun Enterprise Ser ver

System boards and controllers

le0

le1

le2

le3

I/O

le4

le5

I/O

le6

le7

Alternate path (primary path)

FIGURE 1-8 Network Pathgroup

You reference a network pathgroup (for example, to switch from one path to another) by specifying the meta-network interface, for example, apconfig -P mle1 -a le6.

Supported Devices and Software Versions

AP 2.2 supports the Solaris 7 operating environment (32-bit and 64-bit modes). AP supports the following disk arrays:

■ Sun StorEdge™ A5000 and A7000 disk arrays attached to sf ports

■ SPARCStorage Array™ (SSA) disk arrays attached to pln ports on FC-AL SBus

Switch

Host Adapters (SOC controllers)

Alternate path

(active alternate)

Network

The network devices and third party software products supported by AP are listed in the Release Notes Supplement Solaris 7 5/99.

If you alternately path disks, and you also use a volume manager with those disks, the disks must be known to the volume manager by their AP meta-disk names. This requirement enables AP to switch the active path without interfering with the volume manager.

Chapter 1 Introduction to Alternate Pathing 9

You can place the boot disk and the primary network interface under AP control. AP makes it possible for the system to boot unattended even if the primary network or boot disk controller is not accessible, as long as viable alternate paths for these devices are defined.

Example AP Configurations

FIGURE 1-9 shows how you can use AP to support an Ethernet network and a disk

array.

Backplane

Board 1

SBus I/F

FIGURE 1-9 Typical AP Configuration

SBus

Ethernet

Board 2

SBus I/F

SBus

SBus controllers

Fibre channel

In this example, two network controllers—one each on Board 1 and Board 2—are connected to the same network. Similarly, two SSA controllers on the two boards are connected to the same SSA. In this situation, if Board 1 is detached with a DR Detach operation, AP can switch usage to Board 2 without interfering with any I/O operations that may be in progress.

AP is not equivalent to disk mirroring. Disk mirroring primarily achieves data redundancy although two paths are available, one for each side of the mirror. AP achieves true pathing redundancy, by making two paths available for each side of the

10 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

mirror. To use AP and disk mirroring together, you must configure your volume manager software (such as Sun Enterprise Volume Manager

) so that it uses the AP

meta-disk paths. The following figure shows an example of how AP can be used in conjunction with

disk mirroring.

Backplane

Board 1

SBus I/F

SSA

FIGURE 1-10 AP and Disk Mirroring

SBus

Mirrored

Board 2

SBus I/F

Fibre channels

SBus

controllers

SSA

This type of configuration enables you to switch the paths used to implement the mirror from one board to another board, without disrupting the disk mirroring or any active I/O.

AP and Domains

The Sun Enterprise 10000 server supports Dynamic System Domains, or simply “domains.” AP cannot be used across two domains. For example, suppose a board contains a controller that is part of a pathgroup, and you move that board into a different domain using DR. (You can do this only if the alternate path on that board is not currently active.) In this case, you can no longer switch to the alternate path on that board.

Chapter 1 Introduction to Alternate Pathing 11

12 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

CHAPTER

Alternate Pathing Database

This chapter describes how to create and manage the AP database which maintains the state of the AP configuration.

Managing Copies of the Database

AP maintains a database that contains information about all defined meta-disks and meta-networks, and their corresponding alternate paths and properties. One set of data is maintained for each domain on the Sun Enterprise 10000 server. On other Sun Enterprise servers, one set of data is maintained for the entire machine. You should always set up multiple copies of the database. In this way, if a given database copy is not accessible or becomes corrupted, AP can automatically begin to use a current, noncorrupted database copy.

You must dedicate an entire disk partition, one that has at least 300 Kbytes, to each database copy. You can use larger partitions, but doing so wastes disk space. Keep the following information in mind when selecting disk partitions for the AP database:

■ You should set up three to five database copies.

■ As configured at the factory, partition four of the root disk is appropriately sized

for the AP database and is not allocated for any other purposes. This partition is a good choice for an AP database copy, assuming you are not using it for other purposes.

■ The database copies should have no I/O controllers in common with each other.

Following this rule allows maximum availability in case of controller failure.

■ If you have configured your system to make use of Dynamic Reconfiguration

(DR), the database copies should be hosted by I/O controllers on different system boards so that a database copy is accessible if one of the system boards is detached.

■ If you want to place an AP database copy in a partition of an alternately pathed

disk, create two copies of the database using each of the physical paths utilized by the AP meta-disk to access the partition. AP behaves as if two copies of the database exist, when actually there is only one, since the disk is accessible via two paths. The behavior does not result in database inconsistencies, however, since AP always updates and accesses database copies sequentially. This behavior does not result in performance problems since the AP database is not accessed frequently.

On the Sun Enterprise 10000 server, a subset of the information in the AP database is automatically maintained on the SSP for use at boot time. This database contains AP information for the boot disk.

Locating Databases to Maximize RAS

You should consider how you expect to use the system boards that host the I/O controllers for the disks where the AP databases will be stored. If you expect to detach a board often, perhaps because you intend to migrate it between domains, you should probably not place an AP database on any disk attached to a controller hosted by that board. If you do find it necessary to detach such a board, error messages will be sent to the console whenever AP attempts to write to the unavailable database. This does not pose a serious problem. You can re-attach the board at any time, and the stale database is re-synchronized immediately. However, if you attach the board to other domains in the mean time, those domains may write data to the slice that is reserved for the database.

Creating and Deleting Databases

Note – The following AP command examples assume that your command search

path includes the directory where the commands are installed. See “Using SingleUser Mode” on page 41.

14 Sun Enterprise Server Alternate Pathing User’s Guide • May 1999

▼ To Create a Copy of the AP Database

● Use apdb(1M) as follows:

# apdb -c /dev/rdsk/c0t1d0s4 -f

The -c option specifies the raw disk slice (under /dev/rdsk) where you want to create the database copy. You must dedicate an entire disk partition to each database copy. The disk partition must have at least 300 Kbytes.

The -f (force) option is only necessary to create the first AP database copy.

▼ To Delete a Copy of the AP Database

● Use apdb(1M) as follows:

# apdb -d /dev/rdsk/c0t1d0s4 -f # apconfig -D #

The -d option specifies the raw disk slice (under /dev/rdsk) where the copy of the database that you want to delete is located.

The -f (force) option is only necessary to delete the second-to-last copy and the last copy of the database.

In this example, apconfig -D is used after the deletion operation to view information about the existing AP database copies. Since no information is returned, the apdb(1M) command must have deleted the last database copy.

Note – If you delete the last copy of the AP database, the contents of the database

still resides in memory (including all committed and uncommitted entries). If you then create a new copy of the AP database, without rebooting in the interim, the new database contains the same information as the previous database. However, if you reboot after deleting the last copy of the database, the database information in memory is lost. In this case, if you create a new copy of the database, it contains no data.

Chapter 2 Alternate Pathing Database 15

+ 61 hidden pages

Sun Microsystems Sun Enterprise Server User's Guide

Specifications and Main Features

Frequently Asked Questions

User Manual

Preface

Introduction to Alternate Pathing

Purpose of Alternate Pathing

Basic Alternate Pathing Concepts

Physical Path

Meta-Disk

Meta-Network

Disk Pathgroup

Network Pathgroup

Supported Devices and Software Versions

Example AP Configurations

AP and Domains

Alternate Pathing Database

Managing Copies of the Database

Locating Databases to Maximize RAS

Creating and Deleting Databases

▼ To Create a Copy of the AP Database

▼ To Delete a Copy of the AP Database