Windows 2012 Hyper-V pass-through disks and Live Migration support
Since Windows Server 2008 R2 and now with Windows Server 2012, the performance improvements of Fixed and Dynamic disks are impressive. One of the main reasons that some IT folks were still deploying pass-through was due to the disk size limitation to 2TB. But in Windows 2012, with the VHDX format the size limit increased to a huge 64TB and you have features that prevent corruption; plus, by using pass-through disks you lose benefits such as portability, snap-shotting and thin provisioning.
In saying that, as pointed by Jeff Woolsey, Microsoft Windows Server & Cloud:
Pass-through disks are supported during Hyper-V Live Migration ONLY if the Virtual Machine being migrated and the pass-through disk are manage by the same Hyper-V cluster :
Pass through disks are still supported with Windows Server 2012 Hyper-V Live Migration (just like they were with Windows Server 2008 R2 Hyper-V) as long as the migration of a clustered VM and the pass through disk is managed by the cluster.
Pass through disks are not supported for migrations outside of a cluster, such as:
- Shared Nothing Live Migration or
- Using standalone hosts with file on a SMB share (without clustering enabled)
…pass through disks aren’t supported because the pass through disk doesn’t have a way to move between hosts.
Again my recommendation : STAY AWAY FROM PASS-THOUGH DISKS.