Microsoft SQL Cluster Server 2008 R2 on ESXi 5.1 using iSCSI

ESXi 5.1 only supports in guest iSCSI for MSCS shared storage, thus you cannot use RDM from iSCSI luns presented directly to ESXi hosts.

Use of software iSCSI initiators within guest operating systems configured with MSCS, in any configuration supported by Microsoft, is transparent to ESXihosts and there is no need for explicit support statements from VMware

In my test environment, I tested attempting to present iSCSI RDMs to Server 2008 R2 machines. The issue that I was seeing is the test for the cluster was failing sporadically during the storage reservation tests. The issue is that ESXi 5.1 only supports SCSI-3 reservations, but has difficulty with persistent reservations from RDMs. What this will do is cause the cluster to not be able to reserve the volume for a particular node to be able to read/write to it.

My work around was to present the iSCSI volumes directly to the guest's iSCSI initiators. After I did this, the cluster has had zero issues (knock on wood) since I've created the cluster in my production environment.

Update: I saw that ESXi 5.5 now supports RDMs through iSCSI but I have not tested this yet. Will be interesting if I had time to re-design the cluster for Server 2012.

References:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1037959

http://pubs.vmware.com/vsphere-51/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-51-setup-mscs.pdf