dennis9999
Contributor
Contributor

some questions regarding snap shots

I am running version 10 of workstation pro on win 10 host. I am running win xp and win vista quest machines.

To make backups easier and quicker I am looking into using snap shots. I tried it on my xp guest and there are 2 snap shot related files in the quest directory. A 33.9 meg vmsn and a 1K vmsd. The xp files system is 16 gig in size so the file size disparity puzzles me.

1. Why are the snap shot files so small? Can I really recover the entire xp file system with these two files?

2. It only took a minute or two to create the snap shot, seems really fast.

3. I have read that the snap shot files can be moved to another location. Can I do this while the quest is running? Can I them move them back while the guest is running if I need to revert back to that snap shot?

4. I have been suspending each quest and copying the entire directory to an external drive to back them up. The xp system does not take much time but the vista quest is 300gig which takes a good bit of time. I am assuming if either guest will not boot or run then the snap shots cannot be used to recover them and snap shots cannot be used a complete backup/recovery method.

Thanks in advance for your help.

Dennis

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3 Replies
a_p_
Leadership
Leadership

First of all, Snapshots are no backups!

Snapshots in VMware products only contain data blocks which are modified after creating a snapshot. This explains why creating a snapshot is so fast. Snapshots work as a chain, where each chain-link is important (as it only contains deltas).

To answer your questions:

  1. The files you mentioned (.vmsd, .vmsn) only contain metadata, and a memory dump if the snapshot was created while the VM was up and running. The important data is that in the virtual disk (.vmdk) files.
  2. When a snaphsot is created it starts with a small size and grows over time, depending on the modified data.
  3. It's possible to define another location for snapshots, but you cannot move existing snapshots (well you can, but this requires manual work)
  4. As mentioned above, snapshots contain only delta data, and cannot be used without their partent disks.

André

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dennis9999
Contributor
Contributor

Andre:

Thank you for your quick response. I'm still a bit confused as to exactly what a snapshot is good for.

If the quest gets a virus and I have a snapshot before that occurred, do I revert to the snapshot or go back to my last full backup?

If I install some software making the guest unstable, do I revert the snapshot or copy back the most current backup.

Or does a snapshot work like incremental data base backups. You apply the most recent full backup and then apply all the incremental backups since that point and you are now

back to the present data base state before the failure.

Dennis

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a_p_
Leadership
Leadership

Please don't get me wrong. If you have a snapshot, and disaster strikes (like a Virus that hit the VM, or an installation fails), you can certainly revert to a snapshot. However, it's not recommended to keep snapshots for a long time (at least not in a production environment), or use them as a replacement for backups.

Please take a look at https://kb.vmware.com/s/article/1015180​ which explains how snapshots work in VMware products.

André

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