Are you looking to build Windows Failover clusters on VMware vSphere with EqualLogic storage? If so, make sure to use the new EqualLogic Multipathing Extension Module (MEM) for VMware vSphere (assuming you have at least Enterprise licensing). There are several reasons that make the MEM an obvious choice, but let’s first review what the MEM actually is.
In VMware vSphere, there are several native Path Selection Policies (PSP) that handle how the ESX or ESXi hosts connect to the storage infrastructure. For best performance, most use VMware’s native for Round Robin PSP for iSCSI MPIO. This allows you to better utilize all of your NICs rather than keeping the paths in an active/standby configuration. In addition to the native policies, VMware has also opened this up to storage vendors to write their own PSPs to take better advantage of their storage arrays.
Previously only available in vSphere Enterprise Plus, with the release of vSphere 4.1 VMware has reduced the licensing requirement to use vendor supplied PSPs to the Enterprise level. At the same time, Dell released their own PSP for best performance when using EqualLogic SANs.
So why does it make sense to use the MEM and specifically if you’re using Windows Failover Clusters? Here are a few reasons:
1) VMware does not support virtualized Failover Clusters using the native Round Robin policy. They also technically do not support Microsoft clusters on iSCSI storage either, but VMware has stated that that restriction will be going away soon. See this link for more info on virtualizing Microsoft clusters (PDF link).
2) Dell has shown improved performance when using the MEM on virtualized clusters, particularly with Microsoft Exchange 2010 VMs.
3) Installation and configuration of the MEM is very easy and can be configured on a per VMFS volume level. This would allow you to only use the MEM for the VMFS partitions where your clustered VMs reside. That said, the benefits of the MEM extend to non-clustered VMs and should probably be used for all VMFS partitions.