Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)
Reconfiguring a shared disk group is performed with the co-operation of all nodes.
Configuration changes to the disk group happen simultaneously on all nodes and
the changes are identical. Such changes are atomic in nature, which means that
they either occur simultaneously on all nodes or not at all.
Whether all members of the cluster have simultaneous read and write access to
a cluster-shareable disk group depends on its activation mode setting.
The data contained in a cluster-shareable disk group is available as long as at least
one node is active in the cluster. The failure of a cluster node does not affect access
by the remaining active nodes. Regardless of which node accesses a
cluster-shareable disk group, the configuration of the disk group looks the same.
Note: Applications running on each node can access the data on the VM disks
simultaneously. VxVM does not protect against simultaneous writes to shared
volumes by more than one node. It is assumed that applications control consistency
(by using Veritas Storage Foundation Cluster File System or a distributed lock
manager, for example).
Activation modes of shared disk groups
A shared disk group must be activated on a node in order for the volumes in the
disk group to become accessible for application I/O from that node. The ability of
applications to read from or to write to volumes is dictated by the activation mode
of a shared disk group. Valid activation modes for a shared disk group are
exclusivewrite, readonly, sharedread, sharedwrite, and off (inactive).
Note: The default activation mode for shared disk groups is off (inactive).
Special uses of clusters, such as high availability (HA) applications and off-host
backup, can use disk group activation to explicitly control volume access from
different nodes in the cluster.
Table 2-4 describes activation modes for shared disk groups.
Table 2-4
Activation modes for shared disk groups
DescriptionActivation mode
The node has exclusive write access to the disk group. No other node
can activate the disk group for write access.
exclusivewrite
(ew)
49Storage Foundation Cluster File System architecture
About Veritas Volume Manager cluster functionality