HP UX Serviceguard Storage Management Software manual Activation Modes for Shared Disk Groups

NOTE

NOTE

Table 2-2

Cluster File System Architecture

About Veritas Cluster Volume Manager Functionality

Whether all members of the cluster have simultaneous read and write access to a cluster-shareable disk group depends on its activation mode setting as described in Table 2-2, “Activation Modes for Shared Disk Groups.” 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.

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 for 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 Table 2-2, “Activation Modes for Shared Disk Groups.”

The default activation mode for shared disk groups is off (inactive).

Special use clusters, such as high availability (HA) applications and off-host backup, can employ disk group activation to explicitly control volume access from different nodes in the cluster.

Activation Modes for Shared Disk Groups

Activation Mode	Description
exclusivewrite	The node has exclusive write access to the disk group. No other
	node can activate the disk group for write access.
readonly	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	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.
sharedwrite	The node has write access to the disk group.
off	The node has neither read nor write access to the disk group.
	Query operations on the disk group are permitted.

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