Un excellent article sur la live migration et la mise en œuvre de CSV sur Windows Server 2008 R2. A lire absolument

 
A noter le point important sur l’utilisation des snapshots
 

Snapshots and virtual machines

You should avoid taking a snapshot of a running virtual machine. If you revert back to a snapshot of a running virtual machine, the memory state is restored in addition to the disk. Before reverting a clustered virtual machine back to a snapshot, you should first shut down the virtual machine from Failover Cluster Manager, take a snapshot of the virtual machine, and restart the virtual machine.