One of the Microsoft guys has posted about how Hyper-V Server 2008 R2 will continue to be free but it will also include CSV and Live Migration (aka VMotion) included. Hyper-V Server 2008 does not have cluster functionality so you must use Windows Server 2008 Enterprise/Data Center Edition to get this functionality.
Cluster Shared Volume overcomes the shared nothing principle of shared cluster disks by delegating read/write access to individual files to Hyper-V hosts (physical cluster members). This means you can have many virtual machines on a single disk and they can run on many hosts in the cluster. It’s not required for Live Migration but it is strongly recommended. I’m looking forward to it to simplify my disk management. The current version of Hyper-V doesn’t require (it does with VMM 2008) but should have 1 VM per 1 LUN – this allows VM’s to run on any host; the disk ties a VM to the host.
Live Migration finally gives Hyper-V a VMotion style of VM failover where a VM is “offline” for 10 milliseconds (not noticeable) when it is migrated from host 1 to host 2. I’ve recently posted a PowerPoint slide deck that explains this. I’ll be doing a presentation on this online on April 30th.