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About CVM

Review CVM configuration differences from VxVM and CVM recovery operations. For introductory information on CVM, see Cluster Volume Manager.

CVM configuration differences

CVM configuration differs from VxVM configuration in these areas:

• Configuration commands occur on the master node.
• Disk groups are created (could be private) and imported as shared disk groups.
• Disk groups are activated per node.
• Shared disk groups are automatically imported when CVM starts.

CVM recovery

When a node leaves a cluster, it can leave some mirrors in an inconsistent state. The membership change is communicated through GAB to the vxconfigd daemon, which automatically calls the vxrecover utility with the -c option when necessary.

CVM supports both the FastResync option and dirty region logging (DRL) as optional features to improve resynchronization performance. FastResync improves performance when reorganizing volumes (moving, splitting, and joining disk groups). This is useful when performing off-host processing. DRL speeds up resynchronization after a node failure.

Special considerations exist when using the DRL in an SF Oracle RAC environment. As in a non-clustered environment, the DRL in clusters exists on a log subdisk in a mirrored volume. The size of the DRL in clusters is typically larger than in non-clustered systems. The log size depends on the volume size and the number of nodes. The vxassist command automatically imports a sufficiently large DRL.

You can reimport a private disk group as a shared disk group but the DRL for any mirrored volume in the disk group is probably too small to accommodate maps for all the cluster nodes. Adding nodes to the cluster can also result in too small a log size. In this situation, VxVM marks the log invalid and performs full volume recovery instead of using DRL.