I was having a conversation with one of our tech support guys (Greg Williams) recently about the relaxation on the requirement to allow Raw Device Mappings (RDMs) to be presented to different hosts using different SCSI identifiers and still do vMotion operations in vSphere 5.5. You can read that post here where I described how the restriction has been relaxed. Greg mentioned that he was handling a case where customers wished to share a physical mode/passthru RDM between VMs on different ESXi hosts with a view to running Microsoft Clustering Services (MSCS) on top. We call this CAB or Clustering…
When setting up a Microsoft Cluster with nodes running in vSphere Virtual Machines across ESXi hosts, I have come across folks who have experienced Incompatible device backing specified for device ‘0’ errors. These are typically a result of the RDM (Raw Device Mapping) setup not being quite right. There can be a couple of reasons for this, as highlighted here. Different SCSI Controller On one occasion, the RDM was mapped to the same SCSI controller as the Guest OS boot disk. Once the RDM was moved to its own unique SCSI controller, it resolved the issue. Basically, if the OS disk…