It seems difficult to find a solid answer to this question. VMs are running on vSphere 5.5 across multiple ESXi hosts. VMware documentation says both physical and virtual are supported in this configuration but physical is recommended. The same documentation also states, "Clusters across physical machines with non-pass-through RDM is supported only for clustering with Windows Server 2003. It is not supported for clustering with Windows Server 2008." But I am interested in 2012 R2. Main reason I am looking to use virtual RDM is to run native Veeam backups. I am not overly thrill having to use the Veeam agent backup due to limitations and relying on Microsoft's VSS writer. Anyone know what is officially supported by both VMware and Microsoft, and what works best especially when you want to run snapshot based backups? Also, the clustering is being used on file servers.