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What’s New in 2008 R2 – Live Migration

I can’t think of any feature we’ve been asked more in regards to Hyper-V has been around Live Migration, known as VMotion in the VMWare world. Hyper-V R2 now supports Live Migration, partly due to Cluster Shared Volumes.

Live Migration allows a virtual machine to be moved from one node in a cluster, to another node without any downtime.

Image courtesy of Microsoft Corporation

In a nutshell Live Migration accomplishes this by…

Using SCVMM 2008 (an update will be required) you initiate a Live Migration from the source host to another node in the cluster.
Once initiated, a virtual machine is created on the target host. Since the VHD(s) is stored on a CSV there is no copy of a VHD over the network.
Once the VM is created on the target host the data stored in the source hosts RAM is copied to the RAM in the target host. In essence Hyper-V is mirroring the contents of memory on both hosts.
Up until the memory “mirror” is complete, clients continue to be connected to the original VM on the source host.
Once the memory “mirror” is complete, clients are redirected to the VM on the target host.

Now one thing to remember is that both nodes of the cluster need to be online. This is not a DR solution, although the VMs can be made highly available. In a DR situation where the source node fails, the highly available VMs will be restarted on the other node(s) in the cluster.