HP UX Serviceguard Storage Management Software manual Limitations of Shared Disk Groups

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Cluster File System Architecture

About Veritas Cluster Volume Manager Functionality

contact a disk, it should contact another node to check on the disk’s status. If the disk fails, no node can access it and the nodes can agree to detach the disk. If the disk does not fail, but rather the access paths from some of the nodes fail, the nodes cannot agree on the status of the disk. Either of the following policies for resolving this type of discrepancy may be applied:

Under the global connectivity policy, the detach occurs cluster-wide (globally) if any node in the cluster reports a disk failure. This is the default policy.

Under the local connectivity policy, in the event of disks failing, the failures are confined to the particular nodes that saw the failure. However, this policy is not highly available because it fails the node even if one of the mirrors is available. Note that an attempt is made to communicate with all nodes in the cluster to ascertain the disks’ usability. If all nodes report a problem with the disk, a cluster-wide detach occurs.

Limitations of Shared Disk Groups

The cluster functionality of VxVM does not support RAID-5 volumes, or task monitoring for cluster-shareable disk groups. These features can, however, be used in private disk groups that are attached to specific nodes of a cluster. Online relayout is supported provided that it does not involve RAID-5 volumes.

The root disk group cannot be made cluster-shareable. It must be private.

Only raw device access may be performed via the cluster functionality of VxVM. It does not support shared access to file systems in shared volumes unless the appropriate software, such as the HP Serviceguard Storage Management Suite, is installed and configured.

If a shared disk group contains unsupported objects, deport it and then re-import the disk group as private on one of the cluster nodes. Reorganize the volumes into layouts that are supported for shared disk groups, and then deport and re-import the disk group as shared.

Chapter 2

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Contents Second Edition Legal Notices Contents Troubleshooting Cluster Volume Manager AdministrationPrinting History Printing HistoryPage Technical Overview Cluster File System Design Overview of Cluster File System ArchitectureCluster File System Failover Group Lock ManagerCFS Supported Features Supported FeaturesVxFS Functionality on Cluster File Systems CFS Unsupported Features Unsupported FeaturesCFS Unsupported Features Benefits and Applications Advantages To Using CFSWhen To Use CFS Benefits and Applications Chapter Cluster File System Architecture Role of Component Products Veritas Cluster Volume Manager FunctionalityCluster Communication Membership PortsCluster File System and The Group Lock Manager About CFSAsymmetric Mounts Primary and Secondary Mount Options Parallel I/OCluster File System Backup Strategies Synchronizing Time on Cluster File Systems Error Handling PolicyDistributing Load on a Cluster File System TuneablesExample of a Four-Node Cluster About Veritas Cluster Volume Manager FunctionalityPrivate and Shared Disk Groups Activation Modes for Shared Disk Groups Activation Modes for Shared Disk GroupsAllowed and conflicting activation modes Connectivity Policy of Shared Disk GroupsLimitations of Shared Disk Groups About Veritas Cluster Volume Manager Functionality Chapter Cluster File System Administration Cluster File System Administration Cluster Messaging GAB Cluster Communication LLT Volume Manager Cluster Functionality Overview Cluster and Shared Mounts Cluster File System OverviewAsymmetric Mounts Cluster File System Commands Cluster File System AdministrationGrowing a Cluster File System Time Synchronization for Cluster File SystemsFstab file Distributing the Load on a ClusterCluster File System Administration Snapshots for Cluster File Systems Cluster Snapshot CharacteristicsPerformance Considerations Creating a Snapshot on a Cluster File System# cfsumount /mnt1snap Cluster Volume Manager Overview of Cluster Volume Management Example of a 4-Node Cluster Disk group activation mode restrictions Either of the write modes on other nodes will fail # cfsdgadm display Behavior of Master Node for Different Failure Policies Disk Group Failure PolicyRecovery in a CVM Environment Troubleshooting Inaccessible System Installation IssuesIncorrect Permissions for Root on Remote System Resource Temporarily UnavailableInstallation Issues Unmount Failures Cluster File System ProblemsMount Failures Performance Issues Command FailuresHigh Availability Issues Cluster File System Problems Appendix a