VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Disks in VxVM Clusters
Chapter 7306
Disks in VxVM Clusters
The nodes in a cluster must always agree on the status of a disk. In
particular, if one node cannot write to a given disk, all nodes must stop
accessing that disk before the results of the write operation are returned
to the caller. Therefore, if a node cannot 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. A policy must exist to resolve this
type of discrepancy.
Disk Detach Policies
In order to address the above discrepancy, the following policies (set for a
diskgroup) are provided. These can be set by using the vxedit(1M)
command.
Under the global connectivity policy for shared disk group(s), the detach
occurs cluster-wide (globally), if any node in the cluster reports a disk(s)
failure.
Under local connectivity policy, in the event of disk(s) failing, the failures
are confined to the particular node(s) which saw the failure. Note that an
attempt is made to communicate with all nodes in the cluster to
ascertain the disk(s) usability. If all nodes report a problem with the
disk(s), a cluster-wide detach occurs. This is the default policy.
Disk Group Activation
Disk group activation controls volume I/O capability from differentnodes
in the cluster. It is not possible to activate a diskgroup on a given node if
it is activated in a conflicting mode on another node in the cluster. Table
7-2, Allowed and Conflicting Activation Modes, summarizes the allowed
and conflicting activation modes for shared disk groups, as follows:
Table 7-2 Allowed and Conflicting Activation Modes
Disk group
activated in the
cluster as....
Attempt to activate disk group on another node as....