- The most important consideration is transferring the VHD files from the old server to the new one. I was upgrading the hardware that the VM’s were running on, so I needed to transfer the VM’s onto a USB hard drive, upgrade the server and move them back.
There are a couple of things to consider. Firstly, large VM’s take AGES to move! So be prepared to sit an wait a long time. Secondly, ensure you have multiple copies of the VM’s. I had a VM become corrupted on a USB drive and it was just luck that I had another copy on my PC.

- Remember to enable DEP (called a bunch of different things in different BIOS versions) in your servers BIOS. Hyper-V will install successfully and you can start to import VM’s – however they won’t start until you have enabled DEP.

- You need to start any Server 2008 VM’s with a Legacy NIC. This is for a couple of reasons: 1. You need to update the HAL on the VM before Server 2008 will recognize the new hardware. 2. You will have access to the VM remote connection via Hyper-V manager but as the VM tools aren’t installed yet you won’t have mouse access to enable the HAL lookup. The only way around these is to start the VM with a Legacy NIC and then run the HAL & VM tools.

- Don’t use VMM to import the VHD files. VMM creates a copy of the VM’s and takes a long time to process. Import the VM’s via the basic Hyper-V manager and then configure the extra settings via VMM.

- Double check the CPU settings. This is important as one of the migrated VM’s was set to use a maximum 25% of a CPU and the server was really slow. It must have just brought across a strange setting from Virtual Server 05.

- Finally, ensure you run Windows Updates on your VM’s after the move. There are a couple of updates that improve the performance of Hyper-V.

I’ve just completed the migration, so if you have any questions regarding the process feel free to add some comments.