HP Veritas Storage Foundation Administrator's Guide

Veritas Storage Foundation™ 5.0

Cluster File System

Administration Guide Extracts

for the HP Serviceguard

Storage Management Suite

Second Edition

Manufacturing Part Number: T2771-90045

April 2008

Legal Notices

copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor’s standard commercial license.

The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.

Logo, Veritas, and Veritas Storage Foundation are trademarks or registered trademarks of Symantec Corporation or its affiliates in the U.S. and other countries. Other names may be trademarks of their respective owners.

1. Technical Overview

Overview of Cluster File System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Cluster File System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Cluster File System Failover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Group Lock Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

VxFS Functionality on Cluster File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Supported Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Unsupported Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Benefits and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Advantages To Using CFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

When To Use CFS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2. Cluster File System Architecture

Role of Component Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Cluster Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Membership Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Veritas‘ Cluster Volume Manager Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

About CFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Cluster File System and The Group Lock Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Asymmetric Mounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Parallel I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Cluster File System Backup Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Synchronizing Time on Cluster File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Distributing Load on a Cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

File System Tuneables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Single Network Link and Reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

I/O Error Handling Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

About Veritas Cluster Volume Manager Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Private and Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Activation Modes for Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Connectivity Policy of Shared Disk Groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Limitations of Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Contents

3. Cluster File System Administration

Cluster Messaging - GAB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Cluster Communication - LLT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Volume Manager Cluster Functionality Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Cluster File System Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Cluster and Shared Mounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Cluster File System Primary and Cluster File System Secondary . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Asymmetric Mounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Cluster File System Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Cluster File System Commands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Time Synchronization for Cluster File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Growing a Cluster File System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

The fstab file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Contents

Distributing the Load on a Cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Snapshots for Cluster File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Cluster Snapshot Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Performance Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Creating a Snapshot on a Cluster File System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4. Cluster Volume Manager Administration

Overview of Cluster Volume Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Private and Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Activation Modes for Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Connectivity Policy of Shared Disk Groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Disk Group Failure Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Limitations of Shared Disk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Recovery in a CVM Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

A. Troubleshooting

Installation Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Incorrect Permissions for Root on Remote System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Resource Temporarily Unavailable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Inaccessible System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Cluster File System Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Unmount Failures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Mount Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Command Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Performance Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

High Availability Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Preface

The Veritas Storage Foundation™ 5.0 Cluster File System Administration Guide Extracts for the HP Serviceguard Storage Management Suite contains information extracted from the Veritas Storage Foundation Guide - 5.0 - HP-UX, which has been modified to support the HP Serviceguard Storage

Management Suite bundles that include the Veritas Storage Foundation™ Cluster File System by Symantec and the Veritas Storage Foundation™ Cluster Volume Manager by Symantec.

Printing History

The last printing date and part number indicate the current edition.

Table 1 Printing History

™

Cluster File System Administration

Printing

Date

June 2007 T2271-90034 First

January 2008

April 2008 T2271-90045 Second

Part

Number

T2271-90034 Reprint

Edition Changes

Edition

First Edition

Edition

Original release to support the HP Serviceguard Storage Management Suite A.02.00 release on HP-UX 11i v2.

CFS nested mounts are not supported with HP Serviceguard

Second edition to support the HP Serviceguard Storage Management Suite version A.02.00 release on HP-UX 11i v3

1 Technical Overview

This chapter includes the following topics:

• “Overview of Cluster File System Architecture” on page 8

• “VxFS Functionality on Cluster File Systems” on page 9

• “Benefits and Applications” on page 12

HP Serviceguard Storage Management Suite (SG SMS) bundles provide several options for clustering and storage. The information in this document applies to the SG SMS bundles that include the Veritas Storage Foundation™ 5.0 Cluster File System and Cluster Volume Manager by Symantec:

• SG SMS version A.02.00 bundles T2775CA, T2776CA, and T2777CA for HP-UX 11i v2

• SG SMS version A.02.00 Mission Critical Operating Environment (MCOE) bundles T2795CA, T2796CA, and T2797CA for HP-UX 11i v2

• SG SMS version A.02.00 bundles T2775CB, T2776CB, and T2777CB for HP-UX 11i v3

• SG SMS version A.02.00 High Availability Operating Environment (HAOE) bundles T8685CB, T8686CB, and T8687CB for HP-UX 11i v3

• SG SMS version A.02.00 Data Center Operating Environment (DCOE) bundles T8695CB, T8696CB, and T8697CB for HP-UX 11i v3

SG SMS bundles that include the Veritas Storage Foundation Cluster File System (CFS) allow clustered servers running HP-UX 11i to mount and use the same file system simultaneously, as if all applications using the file system are running on the same server. SG SMS bundles that include CFS also include the Veritas Storage Foundation Cluster Volume Manager (CVM). CVM makes logical volumes and raw device applications accessible throughout a cluster.

As SG SMS components, CFS and CVM are integrated with HP Serviceguard to form a highly available clustered computing environment. SG SMS bundles that include CFS and CVM do not include the Veritas™ Cluster Server by Symantec (VCS). VCS functions that are required in an SG SMS environment are performed by Serviceguard. This document focuses on CFS and CVM administration in an SG SMS environment.

For more information on bundle features, options and applications, see the Application Use Cases for the HP Serviceguard Storage Management Suite White Paper and the HP Serviceguard Storage Management Suite Release Notes at:

http://www.docs.hp.com - select “High Availability”, then select “HP Serviceguard Storage Management Suite”

Chapter 1

Technical Overview

Overview of Cluster File System Architecture

CFS allows clustered servers to mount and use the same file system simultaneously, as if all applications using the file system are running on the same server. CVM makes logical volumes and raw device applications accessible throughout a cluster.

Cluster File System Design

Beginning with version 5.0, CFS uses a Symmetric architecture in which all nodes in the cluster can simultaneously function as metadata servers. CFS 5.0 has some remnants of the master/slave node concept from version 4.1, but this functionality has changed in version 5.0 along with a different naming convention. The first server to mount each cluster file system becomes the primary CFS node; all other nodes in the cluster are considered secondary CFS nodes. Applications access user data directly from the node they are running on. Each CFS node has its own intent log. File system operations, such as allocating or deleting files, can originate from any node in the cluster.

NOTE The master/slave node naming convention continues to be used when referring to Veritas

Cluster Volume Manager (CVM) nodes.

Cluster File System Failover

If the server designated as the CFS primary node fails, the remaining nodes in the cluster elect a new primary node. The new primary node reads the intent log of the old primary node and completes any metadata updates that were in process at the time of the failure.

Failure of a secondary node does not require metadata repair, because nodes using a cluster file system in secondary mode do not update file system metadata directly. The Multiple Transaction Server distributes file locking ownership and metadata updates across all nodes in the cluster, enhancing scalability without requiring unnecessary metadata communication throughout the cluster. CFS recovery from secondary node failure is therefore faster than from primary node failure.

Group Lock Manager

CFS uses the Veritas Group Lock Manager (GLM) to reproduce UNIX single-host file system semantics in clusters. This is most important in write behavior. UNIX file systems make writes appear to be atomic. This means that when an application writes a stream of data to a file, any subsequent application that reads from the same area of the file retrieves the new data, even if it has been cached by the file system and not yet written to disk. Applications can never retrieve stale data, or partial results from a previous write.

To reproduce single-host write semantics, system caches must be kept coherent and each must instantly reflect any updates to cached data, regardless of the cluster node from which they originate. GLM locks a file so that no other node in the cluster can simultaneously update it, or read it before the update is complete.

Chapter 1

Technical Overview

VxFS Functionality on Cluster File Systems

The HP Serviceguard Storage Management Suite uses the Veritas File System (VxFS). Most of the major features of VxFS local file systems are available on cluster file systems, including:

• Extent-based space management that maps files up to 1 terabyte in size

• Fast recovery from system crashes using the intent log to track recent file system metadata updates

• Online administration that allows file systems to be extended and defragmented while they are in use

Supported Features

The following table lists the features and commands that are available and supported with CFS. Every VxFS online manual page has a Cluster File System Issues section that informs you if the command functions on cluster-mounted file systems, and indicates any difference in behavior from how the command functions on local mounted file systems.

Table 1-1 CFS Supported Features

Features and Commands Supported on CFS

Quick I/O The clusterized Oracle Disk Manager (ODM) is supported with CFS

using the Quick I/O for Databases feature in the following HP Serviceguard Storage Management Suite CFS bundles for Oracle: For HP-UX 11i v2 - T2776CA, T2777CA, T2796CA, and T2797CA For HP-UX 11i v3 - T2776CB, T2777CB, T8686CB, T8687CB, T8696CB, and T8697CB

Storage Checkpoints

Freeze and Thaw

Snapshots Snapshots are supported with CFS.

Quotas Quotas are supported with CFS.

NFS Mounts You can mount cluster file systems to NFS.

Memory Mapping

Concurrent I/O

Storage Checkpoints are supported with CFS.

Synchronizing operations, which require freezing and thawing file systems, are done on a cluster-wide basis.

Shared memory mapping established by the map() function is supported on CFS. See the mmap(2) manual page.

This feature extends current support for concurrent I/O to cluster file systems. Semantics for concurrent read/write access on a file in a cluster file system matches those for a local mount.

Chapter 1

Delaylog The -o delaylog mount option is supported with cluster mounts.

This is the default state for CFS.

Technical Overview

VxFS Functionality on Cluster File Systems

Table 1-1 CFS Supported Features (Continued)

Features and Commands Supported on CFS

Disk Layout Versions

Locking Advisory file and record locking are supported on CFS. For the

Multiple Transaction Servers

See the HP Serviceguard Storage Management Suite Release Notes in the High Availability section at http://www.docs.hp.com for more information on bundle features and options.

CFS supports only disk layout Version 6 and Version 7. Cluster mounted file systems can be upgraded. A local mounted file system can be upgraded, unmounted, and mounted again, as part of a cluster. Use the fstyp -v special_device command to ascertain the disk layout version of a VxFS file system. Use the vxupgrade command to update the disk layout version.

F_GETLK command, if there is a process holding a conflicting lock, the l_pid field returns the process ID of the process holding the

conflicting lock. The nodeid-to-node name translation can be done by examining the /etc/llthosts file or with the fsclustadm command. Mandatory locking and deadlock detection supported by traditional fcntl locks are not supported on CFS.

See the fcntl(2) manual page for more information.

With this feature, CFS moves from a primary/secondary architecture, where only one node in the cluster processes metadata operations (file creation, deletion, growth, etc.) to a symmetrical architecture, where all nodes in the cluster can simultaneously process metadata operations. This allows CFS to handle significantly higher metadata loads.

Unsupported Features

Functionality that is documented as unsupported may not be expressly prevented from operating on CFS, but the actual behavior is indeterminate. HP does not advise using unsupported functionality on CFS, or to alternately mount file systems with unsupported features as local and cluster mounts.

Table 1-2 CFS Unsupported Features

Features and Commands Not Supported on CFS

qlog Quick log is not supported on CFS.

Swap Files Swap files are not supported on CFS.

The mknod command

Cache Advisories

Cached Quick I/O

You cannot use the mknod command to create devices on CFS.

Cache advisories are set with the mount command on individual file systems, but are not propagated to other nodes of a cluster.

This Quick I/O for Databases feature that caches data in the file system cache is not supported on CFS.

Chapter 1

Table 1-2 CFS Unsupported Features (Continued)

Features and Commands Not Supported on CFS

Technical Overview

VxFS Functionality on Cluster File Systems

Commands that Depend on File Access Times

Nested Mounts HP Serviceguard does not support CFS nested mounts.

File access times may appear different across nodes because the atime file attribute is not closely synchronized in a cluster file system. Utilities that depend on checking access times may not function reliably.

Chapter 1

Technical Overview

Benefits and Applications

The following sections describe CFS benefits and some applications.

Advantages To Using CFS

CFS simplifies or eliminates system administration tasks resulting from hardware limitations:

• The CFS single file system image administrative model simplifies administration by allowing all file system management operations, resizing, and reorganization (defragmentation) to be performed from any node.

• You can create and manage terabyte-sized volumes, so partitioning file systems to fit within disk limitations is usually not necessary - only extremely large data farms must be partitioned to accommodate file system addressing limitations. For maximum supported file system sizes, see Supported File and File System Sizes for HFS and JFS available at: http://docs.hp.com/en/oshpux11iv3.html#VxFS

• Keeping data consistent across multiple servers is automatic, because all servers in a CFS cluster have access to cluster-shareable file systems. All cluster nodes have access to the same data, and all data is accessible by all servers using single server file system semantics.

• Applications can be allocated to different servers to balance the load or to meet other operational requirements, because all files can be accessed by all servers. Similarly, failover becomes more flexible, because it is not constrained by data accessibility.

• The file system recovery portion of failover time in an n-node cluster can be reduced by a factor of n, by distributing the file systems uniformly across cluster nodes, because each CFS file system can be on any node in the cluster.

• Enterprise storage arrays are more effective, because all of the storage capacity can be accessed by all nodes in the cluster, but it can be managed from one source.

• Larger volumes with wider striping improve application I/O load balancing. Not only is the I/O load of each server spread across storage resources, but with CFS shared file systems, the loads of all servers are balanced against each other.

• Extending clusters by adding servers is easier because each new server’s storage configuration does not need to be set up - new servers simply adopt the cluster-wide volume and file system configuration.

• For the following HP Serviceguard Storage Management Suite CFS for Oracle bundles, the clusterized Oracle Disk Manager (ODM) feature is available to applications running in a cluster, enabling file-based database performance to approach the performance of raw partition-based databases:

— T2776CA, T2777CA, T2796CA, and T2797CA — T2776CB, T2777CB, T8686CB, T8687CB, T8696CB, and T8697CB

Chapter 1

Technical Overview

Benefits and Applications

When To Use CFS

You should use CFS for any application that requires file sharing, such as for home directories, web pages, and for cluster-ready applications. CFS can also be used when you want highly available standby data in predominantly read-only environments, or when you do not want to rely on NFS for file sharing.

Almost all applications can benefit from CFS. Applications that are not “cluster-aware” can operate and access data from anywhere in a cluster. If multiple cluster applications running on different servers are accessing data in a cluster file system, overall system I/O performance improves due to the load balancing effect of having one cluster file system on a separate underlying volume. This is automatic; no tuning or other administrative action is required.

Many applications consist of multiple concurrent threads of execution that could run on different servers if they had a way to coordinate their data accesses. CFS provides this coordination. These applications can be made cluster-aware allowing their instances to co-operate to balance the client and data access load, and thereby scale beyond the capacity of any single server. In these applications, CFS provides shared data access, enabling application-level load balancing across cluster nodes.

• For single-host applications that must be continuously available, CFS can reduce application failover time, because it provides an already-running file system environment in which an application can restart after a server failure.

• For parallel applications, such as distributed database management systems and web servers, CFS provides shared data to all application instances concurrently. CFS also allows these applications to grow by the addition of servers, and improves their availability by enabling them to redistribute load in the event of server failure simply by reassigning network addresses.

• For workflow applications, such as video production, in which very large files are passed from station to station, CFS eliminates time consuming and error prone data copying by making files available at all stations.

• For backup, CFS can reduce the impact on operations by running on a separate server, while accessing data in cluster-shareable file systems.

Some common applications for CFS are:

• Using CFS on file servers Two or more servers connected in a cluster configuration (that is, connected to the

same clients and the same storage) serve separate file systems. If one of the servers fails, the other recognizes the failure, recovers, assumes the role of primary node, and begins responding to clients using the failed server’s IP addresses.

• Using CFS on web servers Web servers are particularly suitable to shared clustering, because their application

is typically read-only. Moreover, with a client load balancing front end, a Web server cluster’s capacity can be expanded by adding a server and another copy of the site. A CFS-based cluster greatly simplifies scaling and administration for this type of application.

Chapter 1

Technical Overview

Benefits and Applications

Chapter 1

2 Cluster File System Architecture

This chapter includes the following topics:

• “Role of Component Products” on page 16

• “About CFS” on page 17

• “About Veritas Cluster Volume Manager Functionality” on page 21

Chapter 2

Cluster File System Architecture

Role of Component Products

The HP Serviceguard Storage Management Suite bundles that include CFS also include the Veritas™ Volume Manager by Symantec (VxVM) and it's cluster component, the Veritas Storage Foundation™ Cluster Volume Manager by Symantec (CVM). The following sections introduce cluster communication, membership ports, and CVM functionality.

Cluster Communication

Group Membership Atomic Broadcast (GAB) and Low Latency Transport (LLT) are protocols implemented directly on an ethernet data link. They run on redundant data links that connect the nodes in a cluster. Serviceguard and CFS are in most respects, two separate clusters. GAB provides membership and messaging for the clusters and their applications. GAB membership also provides orderly startup and shutdown of clusters. LLT is the cluster communication transport. The /etc/gabtab file is used to configure

GAB and the /etc/llttab creates these configuration files each time the CFS package is started and modifies them whenever you apply changes to the Serviceguard cluster configuration - this keeps the Serviceguard cluster synchronized with the CFS cluster.

file is used to configure LLT. Serviceguard cmapplyconf

Any attempt to directly modify /etc/gabtab and /etc/llttab will be overwritten by cmapplyconf (or cmdeleteconf).

Membership Ports

Each component in a CFS registers with a membership port. The port membership identifies nodes that have formed a cluster for the individual components. Examples of port memberships include:

port a heartbeat membership port f Cluster File system membership port u Temporarily used by CVM port v Cluster Volume Manager membership port w Cluster Volume Manager daemons on different nodes communicate

with one another using this port.

Port memberships are configured automatically and cannot be changed. To display port memberships, enter the gabconfig -a command.

Veritas™ Cluster Volume Manager Functionality

A VxVM cluster is comprised of nodes sharing a set of devices. The nodes are connected across a network. CVM (the VxVM cluster component) presents a consistent logical view of device configurations (including changes) on all nodes. CVM functionality makes logical volumes and raw device applications accessible throughout a cluster. CVM enables multiple hosts to concurrently access the logical volumes under its control. If one node fails, the other nodes can still access the devices. You configure CVM shared storage after the HP Serviceguard high availability (HA) cluster is configured and running.

Chapter 2

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