VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Cluster Functionality Overview
Chapter 7298
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 or write to volumes is dictated by the
activation mode of the disk group. Valid activation modes for a shared
disk group are exclusive-write , shared-write , read-only ,
shared-read and off (or inactive, as shown in Table 7-1, “Activation
Modes for Shared Disk Group.”
Special uses of clusters, such as high availability (HA) applications and
off-host backup, can utilize disk group activation to explicitly control
volume I/O capability from different nodes in the cluster. Use of
activation modes is described in “Disk Group Activation”.
Table 7-1 Activation Modes for Shared Disk Group
Exclusive write The node has exclusive write access to the disk
group. No other node can activate the dg for write
access.
Shared write The node has write access to the disk group.
Read only The node has read access to the disk group and
denies write access for all other nodes in the cluster.
The node has no write access to the disk group.
Attempts to activate a disk group for either of the
write modes on other nodes will fail.
Shared read The node has read access to the disk group. The node
has no write access to the disk group, however other
nodes can obtain write access.
Off The node has neither read nor write access to the
disk group. Query operations on the disk group are
permitted.
Notes:
• The striped mirror volumes, task monitor, and online relayout
features are not supported in clusters.
• The Volume Manager cluster feature does not currently support
RAID-5 volumes in cluster-shareable disk groups. RAID-5 volumes
can, however, be used in private disk groups attached to specific
nodes of a cluster.
• If a disk group that contains unsupported objects is imported as
shared, deport the disk group. Reorganize the contained volumes
into supported layouts, and then reimport it as shared.