Local detach policy

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 any node, the usual I/O recovery operations are performed to repair the failure, and additionally all the nodes are contacted to see if the disk is still accessible to them. If the write failure is local, and only seen by a single node, I/O is stopped for the node that first saw the failure, and an error is returned to the application using the volume. The write failure is global if more than one node sees 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.

The vxdg command can be used to set the disk detach policy on a shared disk group.

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: Cluster behavior under I/O failure to a mirrored volume for different disk detach policies

Type of I/O failure

Local (diskdetpolicy=local)

Global (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.

Failure of paths to all disks in a volume for a single node

I/O fails for the affected node.

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

Failure of one or more disks in a volume for all nodes.

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

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

More Information

Setting the disk detach policy on a shared disk group