Please read the post by John Howard that talks about an incorrect warning when you try to upgrade to Windows Server 2008 R2 RC. The warning incorrectly advises you to remove the Hyper-V role before performing the upgrade. You will lose all of your Hyper-V configuration if you do this. You’ll also lose your VM configurations because you haven’t done an export in order to be able to do an import.
John also states that you need to remove your snapshots before doing the upgrade because W2008 snapshots are not compatible with W2008 R2 snapshots. Eek!
Normally we advise against in-place upgrades. It’s normally better to go with clean installations followed by a migration. However, that’s not going to be reasonable in a virtualisation environment because the hardware is so huge and expensive. Imagine asking for a cluster of new hardware every 2 years when you virtualised to save money!?!?!? In place upgrades of Hyper-V hosts will be the norm unless hardware is outdated.
There’s going to be some fun moving from dedicated per VM disks to Cluster Shared Volume (CSV) in the W2008 R2 upgrade. I don’t have the hardware to play with this but I can see an offline relocation of each VM into the CSV. That’s going to be “big bang” if you have lots of spare disk in your SAN or gradual if you don’t and need to reallocate disk space.
I was talking to HP’s local top partner, Redstone, last week with a HP rep about storage options. The EVA range is introducing an oversubscription model for their disk storage. Combine this with CSV and dynamic VHD’s and you’ve got some real storage space savings possibilities.