Mental Ward

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Quick Migration: Not Quick Enough? has a graphic demonstration of what you could be in for with Microsoft's Hyper-V in terms of Quick Migration. In Microsoft's world, Quick Migration means that when you move a VM from one physical server to another, it happens almost -- but not quite -- instantly, with minimal downtime. In fact, the VM does go offline, if only for a short time. On the other hand, VMware's Live Migration (in its ESX and ESXi) is an instantaneous transfer, with no downtime, loss of data, state information, and so on.

Now, the first thing to note about this video is the source -- it's from "VMware TV." That will give you a clue, from the outset, that this might be a setup for failure.

With that caveat in mind, it's a fascinating demo. It shows a Quick Migration of a Windows Server 2003 VM from one physical machine to another. At the same time, a Microsoft Dynamics client is trying to access a database residing on the VM. Through a constant ping of the VM, we can see how a) the connection to the VM is dropped for a time, and b) how the Dynamics client fails in its attempt to get the database information (an error box pops up, showing a TCP failure). Shortly thereafter, another popup informs us that the VM has actually been deleted! It's re-started a few moments later. In addition, a network file copy that was initiated on the VM also failed during the Quick Migration.

The video is, naturally, a worst-case scenario, but from what I saw, it could (and will) happen sometimes. The question for those considering Hyper-V is whether these types of interruptions would happen often enough to impact your business. After all, the Dynamics client will retrieve the information after the migration is done, so it's not like you'll never be able to access it (after the user re-initiates, though. That's an aggravation). Same with the file copy; just re-start the copy after the VM restarts. You won't have to wait a day, an hour, or even five minutes to do the task; but you will have to start it all over again.

My assignment/question to you: watch the demo, and tell me what you think. Does this impact your thinking on the validity of Hyper-V in your environment? Why or why not? I'll post your feedback, unless you specifically ask me not to.

Posted by Keith Ward on 04/20/2008 at 12:48 PM


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