Hyper-V Live Migration Details…
We’ve released a Live Migration White Paper. The paper quickly summarizes all of the new features expected in Hyper-V for Windows Server 2008 R2, and then it digs into Live Migration. The White Paper is here. Hyper-V in Server 2008 provides Quick Migration. Quick Migration will move a virtual machine from one host to another, but it creates a few (10 –60) seconds of downtime. R2 includes Live Migration. What’s the difference? I’m stealing from the White Paper:
Quick Migration is a feature of both Windows Server® 2008 Hyper-V™ and Windows Server® 2008 R2 Hyper-V™. Live migration and Quick Migration both move running VMs from one Hyper-V™ physical computer to another, the primary difference is that Quick Migration saves, moves and restores a VM which results in some downtime. The live migration process uses a different mechanism for moving the running VM to the new physical computer. This process will be explained in greater detail in the Live Migration Architecture section of this document.
I had setup a Windows Server 2008 Hyper-V cluster so that I could test Quick Migration and it didn’t work for me because my machines had different processor types. According to the White Paper, both physical hosts must have processors from the same processor manufacturer. I had two AMD processors, one was a dual 
core and the other was a quad core. Quick Migration failed with an error citing different processors. This confused me a bit, so I asked for some clarification…
I was told that migration between machines with the same CPU manufacturer should work, but that you also need to be aware of the features of each CPU. Check out this link on the Intel site. Take note that some of the CPUs have SSE4 available, and others do not. We do expose the true CPU features to each VM, we do not expose a “virtual" CPU” so if your VM is currently taking advantage of SSE4 and the CPU your migrating to does not support SSE4, you will have a problem.
To summarize, the CPUs in each machine in a cluster do not have to be identical, but they at least need to be from the same CPU manufacturer and the more “similar in functionality” they are, the more successful you will be.
If you just want the step by step on how to setup Live Migration, check out:
Hyper-V: Step-by-Step Guide to Using Live Migration in Windows Server 2008 R2
Until next time,
Rob!