While looking over some of the new vSphere 4.1 documentation I noticed that VMware had updated their Setup for Failover Clustering and Microsoft Cluster Service document. As clustering becomes a bigger component of Microsoft’s enterprise applications, support for clustering in vSphere becomes even more important.
As in previous versions of this document they list the limitations for clustering on vSphere. The list of limitation is below:
The following environments and functions are not supported for MSCS setups with this release of vSphere:
Migration with vMotion of clustered virtual machines.
The section above states that migration of clustered VMs with vMotion is unsupported. This isn’t really a surprise as Microsoft clusters tend to be very sensitive to even brief interruptions in networking. Typically during vMotion a ping is dropped and that could cause the cluster to failover unexpectedly. Yet in this release of vSphere vMotion has been enhanced and now supports many more concurrent vMotion operations and also completes much faster. You might think those changes would make it easier to vMotion a cluster node and thus it would be supported. Seems like VMware thought that too.
In this VMware KB on changes to vMotion in vSphere 4.1, they state the following:
MSCS clustered virtual machines can vMotion in a DRS cluster.
One document says you can vMotion a clustered VM and another says you can’t. Which is correct? There is likely just a disconnect between when some of these documents were updated prior to the release of vSphere 4.1. I suspect that it is actually supported and that the vSphere 4.1 MS clustering guide will eventually be updated.
I’ve had trouble in the past using vMotion on cluster nodes (especially big SQL and Exchange clusters) so I’m less inclined to do it even if it is supported. That said, I’d like to see confirmation on whether or not it is supported either way.