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VMware \ Hyper-V Snapshots – the truth, the whole truth and nothing but the .. uh.. truth.. (I guess)

May 9, 2009

I saw a post the other day regarding comments on Hyper-V snapshots. I love things like this – open conversation and opinion is good, as ultimately the truth will be discovered 🙂

Anyway, here was the original post taken from vCriticals website (great site by the way Eric, please “Keep it up” !!) and a response from Matt McSpirit, the Microsoft champion for Hyper-V here in the UK. Lets remember that this is opinion from both sides of the fence. Lets all play nice hey? 🙂

The current snapshot abilities (not to be mixed with VCB) are very similar in the 2 platforms.  As soon as you create a snapshot, a differencing disk (in the Hyper-V world) and a delta vmdk (in the ESX world), are created, and as you continue to snapshot, the disks get daisy chained together and so on.

 Neither VMware or Hyper-V snapshots are for production in the sense that you’d use them in place of a backup technology – they are indeed very useful to test say, an app installation, or a patch upgrade, and yes, on the Hyper-V side, if you want to roll all those differencing snapshots back into the original, you need to delete them (which equates to a merge), shut the VM down, and wait until they are merged in.  I’ve seen documentation on VMware’s side that suggests you shouldn’t VMotion a VM with snapshots unless you commit them all first, and the committing of a VMDK snapshot can take a long time too, just like it can on Hyper-V.

 I’ve found a fair few nightmare stories with large ESX snapshots, like this one: http://communities.vmware.com/thread/73553 where people have waited 2 days for it to merge in.  It seems that the process is faster if you do offline the VM.  It’s obviously also quicker if you keep your snapshots small.  You wouldn’t really want to revert back an Exchange, SQL, Oracle server etc, so I see snapshots really suitable for patching/updates/minor app installs etc, and those snapshots should be quite small, so when you do delete them, and shut down the VM, the merge is pretty quick and seeing as this is more testing than production, the fact that the VM is off for a short time isn’t such an issue.

 So, in essence, I do agree with the article; Snapshots aren’t for production, and if VMware can merge a snapshot(s) whilst the VM is running, then that’s 1-0, but if, as I’ve seen on numerous blog posts, the process sometimes hangs at 95% for ages, rendering that VM unusable from a management/migration/interaction point of view, then neither solution is ideal for production and should be used purely in a test/dev type scenario or for less mission critical applications.

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From → Microsoft

One Comment
  1. Ash permalink

    VMWare can merge and remove snapshots with practically no impact to the VM, I’ve managed to merge a 200gb snapshot with only about 0.5 seconds of machine lag/hanging.
    Though there are some tricks you need to use to make this happen. a detailed understanding of how snapshots are used is required.

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