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

leaves the cluster gracefully, it deports all its imported shared disk groups, but
they remain imported on the surviving nodes.
Reconfiguring a shared disk group is performed with the cooperation of all nodes.
Configuration changes to the disk group are initiated by the master, and 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.
See “Activation modes of shared disk groups” on page 429.
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.
Warning: 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 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).
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 13-1 describes the activation modes.
Table 13-1
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)
429Administering cluster functionality (CVM)
Overview of clustering