Hyper-V Snapshots & VSS Snapshots: the differences
September 17th, 2009 by LinusHi all,
Recently, we’ve seen some confusion about what a Hyper-V Snapshot and what a VSS Snapshot is. The two are very different things!
Hyper-V Snapshot – is a manual snapshot created by the user, to allow you to roll back the entire machine to a past point in time.
- Not VSS Aware and not a backup!
- Only recommended for special occasions –e.g. before a risky operation like attempting an application upgrade, etc.
- Freezes a VHD file, and creates a differencing VHD (AVHD) on top of the VHD.
- Makes it more tedious to migrate from one host to another (but we have instructions on how to do this).
- Major impact on performance.
- Not recommended to leave snapshots hanging around! Remove when you’ve satisfied yourself that it’s no longer needed.
A Hyper-V snapshot is created manually, as shown in the screenshot below:
VSS Snapshot – is a live snapshot created at backup time that makes sure all data is flushed to disk (for database integrity) and ready for backup.
- Exchange logs in guest machines are pruned.
- Slight performance hit as all guests commit their data to disk. Note: All backup apps that use the Hyper-V VSS writer will suffer from this (not just BackupAssist).
VSS Snapshots are turned on by default when you install Guest machines that support VSS (XP and later). They are configured as part of the Integration Services:
BackupAssist uses VSS snapshots to do backups of Hyper-V Guests – this is the proper method of backups.
We highly recommend that you do not use Hyper-V snapshots, or if you must, that you use them for as little time as possible, and then delete the snapshots when finished. Hyper-V Snapshots will slow performance, and also make the recovery process a little more tedious (but certainly not impossible!).
Enjoy!
Linus
I havent read a lot into the whole snap shot thing. But if i was to take a snap shot of a machine, then keep using the machine for a week, have a problem, then try to restore, i would have a problem?
What about if i remove the snapshots after im happy things are OK, how does this affect the long term machine?
The problem with the current version of Hyper-V is, that even if you delete a Hyperv-Snapshot during running VMs it is NOT deleted but instead growing bigger until you actually SHUTDOWN the VM and wait some minutes. Be aware that just rebooting the VM is not deleting the snapshot!
Does the backuptypes (FULL or COPY) required while taking VSS aware snapshots of a HyperV Virtual machine as it is required for Exchange and SQL.