I tested vSphere 6 quite intensively when it was in beta, but I didn’t ever upgrade my lab - basically because I need a stable environment to work on and I wasn’t sure that I could maintain that with the beta.
Now 6 has been GA a while and I have a little bit of time, I have begun the lab upgrade process. You can see a bit more about my lab hardware over on my lab page.
I’ve previously posted around this topic as part of another problem but having had to figure out the process again I think it’s worth re-posting a proper script for this. VMware KB 1016106 is snappily titled “ESXi/ESX hosts with visibility to RDM LUNs being used by MSCS nodes with RDMs may take a long time to boot or during LUN rescan” and describes the situation where booting ESXi (5.1 in my case) takes a huge amount of time to boot because it’s attempting to gain a SCSI reservation on an RDM disk used by MS Clustering Services.