Does Shared-Nothing Migration Mean the Death of the SAN?

You’ve probably heard that Hyper-V in Windows Server 2012 supports what Microsoft is calling “Shared Nothing” live migration. You can see a demo of that here, in a video that was posted on a TechNet blog back in July:

Now don’t get me wrong – the ability to live migrate a running VM from one virtualization host to another across the network with no shared storage behind it is pretty cool. But if you read through the blog post, you’ll also see that it took 8 minutes and 40 seconds to migrate a 16 Gb VM. (And I don’t know about you, but many of our customers have VMs that are substantially larger than that!) On the other hand, it took only 11 seconds to live migrate that same VM running on the same hardware when it was in a cluster with shared storage.

So I will submit that the answer to the question posed in the title of this post is “No” – clearly, having shared storage behind your virtualization hosts brings a level of resilience and agility far beyond what Shared Nothing migration brings. Still, for an SMB that has a small virtualization infrastructure with only two or three hosts and no shared storage, it’s a significant improvement over what they’ve historically had to go through to move a VM from one host to another: That has typically meant shutting the VM down, then exporting it to a storage repository that can be accessed by the other host (e.g., an external USB or network-attached hard drive), then importing it into the other host’s local storage, then booting it up…that can easily take an hour or more, during which time the VM is shut down and unavailable.

So Shared Nothing migration is pretty cool, but, as Rob Waggoner writes in the TechNet post linked above, don’t throw your SANs out just yet.

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