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ccrichard
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Question: What is this Snapshot Space Sorcery?

Post by ccrichard » Jun 15, 2011 11:44 pm

This is a theoretical understanding than a problem question. How is it possible that when I am doing full backups that the snapshots are so small?
For instance, my VMDK is about 40GB but the snapshot vmdk is only like 17MB?

tsightler
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Re: Question: What is this Snapshot Space Sorcery?

Post by tsightler » Jun 16, 2011 1:29 am

A "snapshot" in the VMware world is actually an incredibly simple concept. When you take a snapshot VMware stops writing changes to the original VMDK, and starts writing change blocks to the snapshot.vmdk. As you continue to make changes to the disks in the VM the snapshot.vmdk will grow to contain those changes. If you "delete" the snapshot, the changes a read from the snapshot VMDK and written to the "real" vmdk. If you revert a snapshot you basically just throw the snapshot.vmdk away.

There's plenty of information about VMware snapshots on the internet if you want to know more.

ccrichard
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Re: Question: What is this Snapshot Space Sorcery?

Post by ccrichard » Jun 16, 2011 5:17 pm

Oh, that's right. I think I should have known that. This also explains why it often takes longer to "delete" the snapshot than to create one.
Then, this is not sorcery, it is enlightenment.

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