Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

The activation-mode is one of exclusivewrite, readonly, sharedread,
sharedwrite, or off.
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 the file be consistent on
all nodes in the cluster as in Table 13-2. Otherwise, the results of activation are
unpredictable.
If the defaults file is edited while the vxconfigd daemon is already running, run
the /sbin/vxconfigd -k -x syslog command on all nodes to restart the process.
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
diskgroup command.
See “Listing shared disk groups” on page 454.
You can also use the vxdg command to change the activation mode on a shared
disk group.
See “Changing the activation mode on a shared disk group” on page 458.
It is also possible to configure a volume so that it can only be opened by a single
node in a cluster.
See “Creating volumes with exclusive open access by a node” on page 459.
See “Setting exclusive open access to a volume by a node” on page 459.
Connectivity policy of shared disk groups
A shared disk group provides concurrent read and write access to the volumes
that it contains for all nodes in a cluster. A shared disk group can be created on
any node of the cluster. This has the following advantages and implications:
■ All nodes in the cluster see exactly the same configuration.
■ Commands to change the configuration are sent to the master node.
■ Any changes on the master node are automatically coordinated and propagated
to the slave nodes in the cluster.
431Administering cluster functionality (CVM)
Overview of clustering