HP 3PAR VMware ESX Implementation Guide

Figure 18 vSphere Client
• 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 and
unbalanced state which might yield significant I/O performance issues. HP does not recommend
the Implementation of an MRU path policy.
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 change again.
For additional information on this topic, see the chapter on "Multipathing" in the VMware SAN
Configuration Guide at VMware.
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 on pre-ESX 5.5 hosts, then individually change these specific RDM LUNs from
Round Robin policy to FIXED or MRU path policy.
“LUN Set to Round Robin” (page 42), shows output from a Fibre Channel configuration, a LUN
with a path that was set to Round Robin (VMware).
NOTE: Each path status is shown as Active (I/O). The path status for an iSCSI configuration
would be the same.
Multipath Failover Considerations and I/O Load Balancing 41