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Snapshots That Don't Suck

Hyper-V might be in its infancy, but its snapshot feature shows quite a bit of maturity. Basically, my gripe with most hypervisors is that when they make or remove snapshots, the burden on the guest is noticeable. Hyper-V is not immune to this, but what it does is pretty good. During a snapshot, a dropped ping can cause a problem for non-virtualization-centric notification systems and generate false failures. This can occur while the VM is taking or removing a snapshot.

In working with Hyper-V, I noticed right away is that there was only one lost ping in the snapshots I've taken. There was latency on the subsequent pings, but I saw only the single drop. This is important for production environments where snapshotting is used either as a backup mechanism or done before any sizable change. The only reason I am so focused on the lost ping count during snapshot operations is because of systems that may perceive the guest to be offline. Beyond that, many systems have timeouts for transactions that can be manifested by the slight delay.

And Hyper-V delivers on the other end in that the removal of the snapshot does not cause a lost ping. For VMs that have very large storage, this upfront and backside availability will become important as we will surely see VMs get larger as capabilities increase.

TechNet blogger Robert Larson has a good explanation of snapshotting as a whole and how it applies to Hyper-V but says, "Snapshots do not affect the running state of the virtual machine..." I beg to differ slightly on a technicality. When the snapshots are taken, there is a effect on the guest. Luckily, Hyper-V's implementation is pretty quick.

Snapshots, in most situations are not a key component to the everyday top-level virtualization tasks like VM migration, failover or management. Yet, they're convenient and their usefulness is clear.

Have you used much of Hyper-V’s snapshot functionality? E-mail me with your comments or share them below.

Posted by Rick Vanover on 02/10/2009 at 12:47 PM


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