HP Veritas Volume Manager 5.0 -UX 11i v3 Activation modes of shared disk groups, Readonly ro

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Administering cluster functionality

Overview of cluster volume management

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 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). These activation modes are described in detail in the table “Activation modes for shared disk groups.”

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 13-1	Activation modes for shared disk groups
Activation mode		Description
exclusivewrite (ew)		The node has exclusive write access to the disk group. No
		other node can activate the disk group for write access.
readonly (ro)		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 fail.
sharedread (sr)		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.