Snapshots and Thin Disks

[tmback]

I am fairly new to ESXi, and I have been trying to find the answer to my question, but have had no luck so far. Whenever I take a snapshot of a VM with a Thin disk it automatically converts it to a Thisk disk. Is this normal behavior, and can this be changed.

Thanks!

[DSTAVERT]

Not normal behavior but perhaps I don't understand your problem. The original VMDK is frozen when you take a snapshot and all new writes are to the new snapshot disk as in server-0001.vmdk. The original disk shouldn't change.

[tmback]

Maybe what I am seeing is a bug? If I look at the datastore, the original .vmdk is around 6 GB, the snapshot vmdk is a little over 1 MB, but if I edit settings on that machine and look at the Virtual Disk, it shows Provisioning Type as Thick, and Size 40 GB.

[TomHowarth]

it sounds like a bug, what is the status of the disk after you commit the snapshot? is it still thin provisioned of has it grown?

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Tom Howarth VCP / vExpert

VMware Communities User Moderator

Blog: www.planetvm.net

Contributing author for the upcoming book "[VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment|http://my.safaribooksonline.com/9780136083214]”. Currently available on roughcuts

[tmback]

Although the settings are showing the disk provisioning has changed to thick after a snapshot, the disk has not actually grown when I look at the storage resources. Also, once I create a snapshot, I can no longer adjust the disk size. Maybe I am not doing something correctly. Is there more to taking a snapshot than pressing the take snapshot button, entering a name, and hitting ok?

Just for reference, I am using ESXi 4.0.0 build 171294, vCenter Server 4.0.0 build 162856.

I am curious if anyone else has seen this issue with the same build or could verify what I am observing.

[kjb007]

That is correct. Once you create a snapshot, you can not edit the disk size any longer. If you want to increase the disk size, you will have to committ your snapshots.

-KjB

VMware vExpert

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[tmback]

How do you commit a snapshot? What exactly does commiting a snapshot do?

Thanks!

[kjb007 · Accepted solution]

Commit a snapshot, means deleting the snapshot. Deleting/commiting a snapshot writes all of the snapshot information back into the main disk. You effectively keep your current state, but lose the recovery point. Since snapshots grow without bound, it's generally not good to run on a snapshot for an extended period of time. The longer you wait, the more the snapshot grows, and the longer it takes to committ. The largest snapshot I've had to deal with, grew to ~600 GB, took over 2 days to committ that data, and I wasn't 100% sure it would committ correctly. Worked as advertised though.

-KjB

VMware vExpert

Don't forget to leave points for helpful/correct posts.

[PredatorVI]

I am seeing the behavior described initially in this thread where I have VM's that are all provisioned as "thin", but as soon as I take a snapshot, the properties say it is "thick". We are running ESX 4.0.

It doesn't appear that the disk really becomes thick, unless you try to clone and tell it to keep the disk format the same as the source. At this point, the clone becomes thick.

Cloning a single VM is not the problem as it is simple to just select "thin" when prompted.

The real issue comes when we clone an entire vApp. We are using vApps to group and contain complete testing environments. It is very convenient to clone the entire vApp. However, cloning a vApp does not prompt and ask how to treat the disk formats for the clones within the vApp so it defaults to keeping it the same as the source which it now thinks is "thick"!

Is there a way to change the default behavior for cloning to "thin"? This would solve my problem, even though snapshots are f.u.b.a.r.-ing the disk format.

[DSTAVERT]

You should always create a new post for your problem. The question is marked answered and you risk no one responding since it is already answered. Your issue isn't the same as the the original post and deserves a response.

[PredatorVI]

Ah...didn't notice that. I read through the thread and there seemed to be an outstanding request (or two) to see if anyone else had seen this behavior. Starting a new post now...