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Shared-Nothing Live Migration: Cool, But Not a Game-Changer

Microsoft this week announced a new feature that will be available for Hyper-V version 3 and System Center Configuration Manager 2012: shared-nothing live migration. In so many words, it's the ability to move a virtual machine while it is powered on from one host to another without requiring shared storage.

While I am very excited to see this welcome feature for Hyper-V, which reinforces a much-needed notion of creativity at Microsoft, the feature is not a game changer by any stretch of the imagination. Let's take a look at how it works:

  1. Move the VM virtual disks, snapshots, vm configuration metadata over a standard Ethernet connection
  2. Move the VM state and memory
  3. Delete VM state on original host and complete live migrate to destination host

You can't deny that it is cool and might be appealing to a small subset of customer that are leveraging VMs with small virtual disks, but entertain this scenario for me: a VM with 1 TB virtual disk ... wait, Eli, you are not realistic, you might be thinking ... fair enough -- what about a VM with 500GB virtual disks? Moving that amount of data over a 1 GB Ethernet or even a 10 GB Ethernet is not quick or feasible in most environments, but assuming it was acceptable this would only be used as a maintenance technique which is what it was slated for anyway. To think that you will constantly be copying large virtual disks between hosts is not practical and is not scalable. How many VMs can you move at the same time? What is the impact on the network?

To top it all, you cannot use high availability with this feature, and that makes sense since you need a point of reference for HA to work. How can you recover a VM when its files are on the host that failed? Now maybe in the future they build in replication, but even then, constantly replicating is not easy, scalable or guaranteed. So, for those of you that were dismantling the SAN, not yet folks.

I do want to reiterate, however, that the feature is most certainly innovative and cool and adds value to Hyper-V 3, but I definitely expect VMware, Citrix and Red Hat to respond relatively quickly to such a feature. I am happy, though, that Microsoft is again leading in innovation and others are having to copy features, as opposed to Microsoft playing catch up all the time.

Your thoughts?

Posted by Elias Khnaser on 04/18/2012 at 12:49 PM


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