Understanding Alike’s Restore / Overwrite Behavior
Categories: Restore, XenServer, Hyper-V, Alike v4
For full VM restore jobs, Alike offers you the choice to “Revert Original VM” or “Restore as Copy.”
This KB article provides an explanation of Alike’s restore behavior and options.
By default, Alike will choose “Restore as Copy,” which will create a new VM, named the same as the original with an “-Alike Restore” at the end (e.g. “Server01-Alike Restore”). If a VM with this name already exists on the target host the restore job will fail.
However, you may choose to ‘Revert Original VM’ for your restore job. In this case, Alike will try to find the original VM (on the host server you specify), and revert it to the backup you selected. Please note: Alike finds the ‘original’ VM by name, so if the VM was named “Server01” when the backup was taken, Alike will search for a VM named “Server01” to revert. If Alike does not find a VM to revert, it will perform a regular restore, making a new VM.
When performing a ‘revert’, Alike uses a special type of restore, known as a differential restore. This is an optimized form of restore, where Alike will only write blocks that are different than what currently exist on the VM being restored. This can provide modest to dramatic performance improvements, depending on the amount of differences.
It is also worth noting that there is no requirement that the VM you choose to revert be the same one the backup came from. That is to say, you can ‘revert’ to a different VM, if you like. This can be useful in some cases to speed up your restore time by, for example, restoring on top of a base server image, or similar server clone.