We get more new cool feature if keep virtual hardware up to date. And you may face boot problem when upgrade lower virtual hardware version to latest. I always keep my Microsoft Cluster Services VM (MSCS VM) up to date since RDM disk usually uses on that kind of VMs. I tried to search how to upgrade virtual hardware on MSCS VM with RDM LUN, but no lucky. That's my experience: Update manager doesn't work for MSCS VM. No snapshot would be taken if your SCSI controller of RDM is physical mode, you should have a good backup before upgrading. It's possible to force upgrade hardware version by right click VM and select Upgrade Virtual Hardware . Make sure all services are running on another node. You will get following error message on Event for RDM disks in vSphere Client, upgrading procedure won't be finished until error pop out for all RDM disks. I tried upgrade version 7 to 8.