Recently one of our customers has been playing with Hyper V, creating virtual machines for testing purposes. We have advised them in this and have guided them through using Hyper V, and it’s features and functions. One of the questions asked by the customer was about snapshots. ÔÇÿWhy not use them for backups?’ they asked.
For anyone using Hyper V, Snapshots can be a very handy tool. Allowing the swift roll back of a VM to a previous state, they were intended to be used mainly for development and testing environments. They do have their uses for production environments too however, for example; if you wished to perform a potentially risky update on software installed on a virtual machine a quick snapshot before would allow you to do so safe in the knowledge you can revert to before the update simply by loading the snapshot.
One thing that snapshots should not be used for is a substitute for backups. Although they may on the surface seem ideal for this purpose there are a few reasons this is not recommended.
- They do not provide protection against problems that may occur on the host server (the one running Hyper-V), such as a hardware problems on the physical computer or a software-related issues in the operating system.
- Programs running in the virtual machine will not be aware of the snapshot and when rolling back they will not be able to adjust correctly. For example a Exchange server on a VM which has reverted to a snapshot would expect to have connections to the same clients as it did when the snapshot was created.
- The snapshot files (.avhd) will not work, or at least not you will easily be able to revert to them, once they have been moved from their original location. This means that copying them away from the host machine (as you may if you were planning to use them as a backup) will essentially make them useless.
Please note: Our method of backing up HyperV VM’s involves the use of volume shadow copy snapshots. These are not the same as HyperV snapshots! For more info please see the following:
Hyper-v Backups on the Glo Networks Technical Blog
Hyper-V Snapshots & VSS Snapshots: the differences on the Backup Assist Blog
Hyper V Snapshots FAQ on the Technet site