The KB article that I reported on was incorrect. I’ve since posted
a correction that shows you what the KB article should have said.
I’ve seen lots of posts online where people complain the Live Migration fails on WS2012 Hyper-V when a VM has a pass-through disk. It’s official, Live Migration in WS2012 Hyper-V does not support pass-through disks (what VMware calls Raw Device Mapping).
Changes and improvements in Windows Hyper-V Server 2012 no longer support pass-through disks if Live Migration is to be used.
I, for one, applaud this. I’ve been quite vocal about disliking passthrough disks. If you need the flexibility and the fastest storage performance then use fixed virtual hard disks. A fixed virtual hard disk is almost the same speed as the underlying LUN and you’re probably getting lots of IOPS by stacking disks in a LUN or disk group. Half the Internet (if not more) runs like this, so stop thinking that your mission critical app for 100 users needs to be special – especially if you’re guessing … and I know you haven’t done an assessment. You know who you are.
The default format of virtual hard disk in WS2012 is VHDX. If you need volumes bigger than 2040 GB (just under 2 TB) then VHDX scales out to 64 TB. Seriously, just use VHDX and stop applying inappropriate and limited VMware practices to Hyper-V.