Upgrade testing scenario using snapshots

ESXi 5.5


The end goal is to have a successful upgrade with no snapshots remaining.


Initially there is a Windows VM with no snapshots.




Scenario 1:


I’ll take a snapshot and perform the upgrade on that snapshot.  The upgrade fails.


I’ll simply delete the snapshot and be back at the original VM with no changes.  Correct?



Scenario 2:


I’ll take a snapshot and perform the upgrade on that snapshot.  The upgrade succeeds.


Do I delete the snapshot and perform the upgrade again on the original VM or is there some way to move the changes from the upgrade back to the original VM?


Thanks for any guidance.

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When a snapshot is taken the VM's original base disk files are frozen and a set of new snapshot delta files are created. All changes that occur on the VM are written to these delta files, leaving the base disks consistent with the point in time the snapshot was created. The same process occurs if multiple snapshots are taken; the files the VM is running on are frozen and a new set is created to contain new changes.

If you want to move the machine back to the point in time the snapshot was taken you would open Snapshot Manager, select the relevant snapshot and select "Revert To". The VM will now begin running from the original disk files (previously frozen) and you will be back at the point in time when the snapshot was capture.

Deleting a snapshot causes VMware to consolidate, or merge, the changed data in the delta files with the source disks, leaving you with only the original set of files for the VM.


For Scenario1 you would not want to delete the snapshot, you would want to use the steps I described above to revert to the snapshot you took before installing the upgrade. This takes your VM back to a point in time before the upgrade so you can try it again or leave the VM running in its previous functional (but not upgraded) state. If you just deleted the snapshot you would be left with your broken VM/application with no snapshot to roll back to.

In Scenario2 yes, you would simply delete the snapshot. This would merge the changed blocks in the delta files with the original disks and you are left with a clean, successfully upgraded VM with no snaps.

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