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409Administering cluster functionality
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=leave
Effect 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-mirror or 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.