The ESX host is hosting a passive Microsoft Cluster node. This includes ESX hosts that are exposed to the LUNs used for MSCS but have no virtual machines that participate in Microsoft clustering.
- The virtual machine configured for the Microsoft Cluster uses an RDM. This includes RDMs exposed to the virtual machine with virtual SCSI bus sharing set to either Physical or Virtual.
When ESX hosts a virtual machine in these scenarios, attempts by any ESX host (other than the one that is hosting the Active node) to conduct I/O to the LUNs used by the Microsoft Cluster results in an I/O error. This behavior is expected as the active Microsoft Cluster node maintains a SCSI reservation on the RDM LUNs.
Full article at vmware.com