Dynamic Multi-Pathing 7.3.1 Administrator's Guide - Linux

DMP in a clustered environment

In a clustered environment where Active/Passive (A/P) type disk arrays are shared by multiple hosts, all nodes in the cluster must access the disk through the same physical storage controller port. Accessing a disk through multiple paths simultaneously can severely degrade I/O performance (sometimes referred to as the ping-pong effect). Path failover on a single cluster node is also coordinated across the cluster so that all the nodes continue to share the same physical path.

Prior to release 4.1 of VxVM, the clustering and DMP features could not handle automatic failback in A/P arrays when a path was restored, and did not support failback for explicit failover mode arrays. Failback could only be implemented manually by running the vxdctl enable command on each cluster node after the path failure had been corrected. From release 4.1, failback is now an automatic cluster-wide operation that is coordinated by the master node. Automatic failback in explicit failover mode arrays is also handled by issuing the appropriate low-level command.

See About discovering disks and dynamically adding disk arrays.

For Active/Active type disk arrays, any disk can be simultaneously accessed through all available physical paths to it. In a clustered environment, the nodes do not need to access a disk through the same physical path.