Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

When a shared disk group is created or imported, it is activated in the specified
mode. When a node joins the cluster, all shared disk groups accessible from the
node are activated in the specified mode.
The activation mode of a disk group controls volume I/O from different nodes in
the cluster. It is not possible to activate a disk group on a given node if it is
activated in a conflicting mode on another node in the cluster. When enabling
activation using the defaults file, it is recommended that this file be made identical
on all nodes in the cluster. Otherwise, the results of activation are unpredictable.
Note: If the /etc/default/vxdg file is edited while the vxconfigd daemon is
already running, the vxconfigd process must be restarted for the changes in the
defaults file to take effect.
If the default activation mode is anything other than off, an activation following
a cluster join, or a disk group creation or import can fail if another node in the
cluster has activated the disk group in a conflicting mode.
To display the activation mode for a shared disk group, use the vxdg list
command.
You can also use the vxdg command to change the activation mode on a shared
disk group.
See the Veritas Volume Manager Administrator’s Guide.
Connectivity policy of shared disk groups
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.
Table 2-6 describes the policies for resolving this type of discrepancy.
Table 2-6
Policies
DescriptionPolicy
The detach occurs cluster-wide (globally) if any node in the cluster
reports a disk failure. This is the default policy.
Global
51Storage Foundation Cluster File System architecture
About Veritas Volume Manager cluster functionality