HP QR516B manual Multipath Failover Considerations and I/O Load Balancing

•A path policy of MRU (most recently used) does not maintain or reinstate balancing of I/O load after a failover/failback multipath event. This could leave I/O in an unplanned for and unbalanced state which may yield significant I/O performance issues. Implementation of an MRU path policy is not recommended by HP.

NOTE: If I/O is active to a LUN and an attempt is made to modify the path policy, a failure can occur, indicating:

"error during the configuration of the host: sysinfoException;

Status=Busy: Message=Unable to Set".

If this problem occurs while attempting to change the path policy, reduce the I/Os to that LUN and then try making the desired changes.

For additional information on this topic, refer to the chapter on "Multipathing" contained in the VMware SAN Configuration Guide.

Configuring Round Robin Multipathing on ESX 4.x or later for Fibre Channel

With ESX version 4.0 and later, VMware supports a round-robin I/O path policy for active/active storage arrays such as HP 3PAR StoreServ Storage. A round-robin I/O path policy is the preferred configuration for ESX 4.0 and later; however, this path policy is not enabled by default for HP 3PAR devices.

CAUTION: If you are running Windows Server 2012 or Windows Server 2008 VM Cluster with RDM shared LUNs, then individually change these specific RDM LUNs from Round Robin policy to FIXED or MRU path policy.

“LUN Set to Round Robin” (page 40), which is output from a Fibre Channel configuration, shows a LUN with a path that has been set to Round Robin (VMware).

NOTE: Note that each path status is shown as Active (I/O). The path status for an iSCSI configuration would be the same.

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