Dynamic Multi-Pathing 8.0.1 Administrator's Guide - Windows

DMP in a clustered environment

In a clustered environment, where Active/Passive type disk arrays are shared by multiple hosts, all nodes in the cluster must access the disk by the same physical storage controller port. Accessing a disk by 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. DMP and the clustering feature can handle automatic failback in A/P arrays when a path is restored, and support failback for explicit failover mode arrays. It is 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. 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 all need to access a disk by the same physical path. In clustered environment, DMP selects an alternate path without requiring client application reconnection in case of a storage path failure. In case of server failure, the application is failed over to another cluster node which needs client reconnection. During normal operation, multiple data paths may be employed to provide greater aggregate throughput than one path could provide.