Administering cluster functionality 409

Overview of cluster volume management

The default settings for the detach and failure policies are global and dgdisable respectively. You can use the vxdg command to change both the detach and failure policies on a shared disk group, as shown in this example:

#vxdg -g diskgroup set diskdetpolicy=local dgfailpolicy=leaveEffect of disk connectivity on cluster reconfiguration

The detach policy, previous I/O errors, or access to disks are not considered when a new master node is chosen. When the master node leaves a cluster, the node that takes over as master of the cluster may already have seen I/O failures for one or more disks. Under the local detach policy, if a node was affected before reconfiguration, and this node then becomes the master, the failure is treated as described in “Connectivity policy of shared disk groups” on page 404. Some failure scenarios do not result in a disk group failure policy being invoked, but can potentially impact the cluster. For example, if the local disk detach policy is in effect, and the new master node has a failed plex, this results in all nodes detaching the plex because the new master is unaffected by the policy.

The detach policy does not change the requirement that a node joining a cluster must have access to all the disks in all shared disk groups. Similarly, a node that is removed from the cluster because of an I/O failure cannot rejoin the cluster until this requirement is met.

Limitations of shared disk groups

Note: The boot disk group (usually aliased as bootdg) 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 is installed and configured.

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.

If you have RAID-5 volumes in a private disk group that you wish to make shareable, you must first relayout the volumes as a supported volume type such as stripe-mirroror mirror-stripe. Online relayout of shared volumes is supported provided that it does not involve RAID-5 volumes.

If a shared disk group contains RAID-5 volumes, deport it and then reimport 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 reimport the disk group as shared.