HP Veritas Volume Manager 5.0 -UX 11i v3 Local detach policy, See, Table, Local, Global, ” on page, The table, Type of I/O failure, disk detach policies, (diskdetpolicy=local)

406Administering cluster functionality

Overview of cluster volume management

Local detach policy

Caution: Do not use the local detach policy if you use the VCS agents that monitor the cluster functionality of Veritas Volume Manager, and which are provided with Veritas Storage FoundationTM for Cluster File System HA and Veritas Storage Foundation for databases HA. These agents do not notify VCS about local failures.

The local detach policy is designed to support failover applications in large clusters where the redundancy of the volume is more important than the number of nodes that can access the volume. If there is a write failure on a slave node, the master node performs the usual I/O recovery operations to repair the failure, and additionally contacts all the nodes to see if the disk is still acceptable to them. If the write failure is not seen by all the nodes, I/O is stopped for the node that first saw the failure, and the application using the volume is also notified about the failure. The volume is not disabled.

If required, configure the cluster management software to move the application to a different node, and/or remove the node that saw the failure from the cluster. The volume continues to return write errors, as long as one mirror of the volume has an error. The volume continues to satisfy read requests as long as one good plex is available.

If the reason for the I/O error is corrected and the node is still a member of the cluster, it can resume performing I/O from/to the volume without affecting the redundancy of the data.

See “Setting the disk detach policy on a shared disk group” on page 425 for information on how to use the vxdg command to set the disk detach policy on a shared disk group.

The table, “Cluster behavior under I/O failure to a mirrored volume for different disk detach policies,” summarizes the effect on a cluster of I/O failure to the disks in a mirrored volume:

Table 13-3	Cluster behavior under I/O failure to a mirrored volume for different
	disk detach policies
Type of I/O failure		Local	Global
		(diskdetpolicy=local)	(diskdetpolicy=global)

Failure of path to one disk in a volume for a single node

Reads fail only if no plexes remain available to the affected node. Writes to the volume fail.

The plex is detached, and I/O from/to the volume continues. An I/O error is generated if no plexes remain.