Snapshots: Trying to get a better understanding

[maxi-m]

I'm in the process of trying to use the Standalone Converter to restore "BU" images of a VM that corrupted when I tried to remove snapshots using "Delete All" - the ESXi manual states that "delete all" commits all previous snapshots. I had a number of saved snapshots thinking these could be used as backups - I understand now that this is incorrect. I also understand that "stale" snapshots can cause problems. My snapshot routines also used a tremendous amount of diskspace as well - which I am trying to recover now.

I'm looking for the best method to use snapshots - my current understanding is:

1) Delete a snapshot - consolidates the current changes to disk - ???

2) Revert to snapshot - rolls the system back to that image state - ??? ("stale" snapshots can cause issues as internal id's may have been updated - ex. Kerberos tokens on Windows domains)

Note: I was reading the section on excluding disks from snapshots (independent disk - persistent or non-persistent is this something to consider as well - I've been accepting the defaults for disks)

I'll appreciate any help on this, thanks in advance...

Maxi

[runclear]

I think youve got it down,

Delete Snapshot - Commits changes to the base/main vmdk and deletes the Delta files...

Revert to: pretty self explainatory,

And yes, its really not good practice to leave snapshots laying around.. They are not really ment to serve as 'backups'

Be aware that if you do have your disks set to independant mode, that some things wont work, ie: VCB, Storage Vmotions etc... unless you have a good reason to exclude a disk from being snapshotted....

-

---

[kjb007]

Snapshots should be used for temporary "backup" functionality only. When you create a snapshot, a new disk file is created on the VMFS, and all changes to disk are written to this "log" as opposed to being integrated into the original vm disk itself. This snapshot disk usage is not capped, and can grow unchecked until you run out of space completely. Every time you create a snapshot, a new disk file is created, so multiple snapshots, creates multiple files which are not written to.

Deleting a snapshot causes that snapshot's log file to be written / consolidated to the snapshot or disk previous to it.

Reverting to a snapshot will either create a new snapshot or remove the data from your current snapshot back to the point of the snapshot you are reverting to.

Snapshots should really be used for temporary recoverability of machines, for instances, during a patch upgrade, or an OS upgrade, that can easily be reverted.

-KjB

VMware vExpert

[COdlk · Accepted solution]

Here is a good KB that gives an overview of snapshots

http://kb.vmware.com/kb/1009402

david

[maxi-m]

All,

Thanks for the excellent responses. One last question: In the KB article it states "Warning: All data associated with the deleted snapshot is permanently lost." Does that mean that deleting the snapshot will only affect the data state at "that" timestamp and will not affect the system current data state.

For example: I have a web application running on this VM - I add a new module and take a snapshot... the module works without issue and make a few minor modifications - the next day I'm good with the changes and "Delete" the snapshot. The machine will remain at the current state and the snapshot diskspace will be recovered. I just want to be clear on using the snapshot feature.

Thanks,

Maxi

[kjb007]

That is correct. It pretty much means that you can no longer go back to that point when you took the snapshot. You're basically accepting where you are.

-KjB

VMware vExpert