Hyper-V Snapshots. What are they?  When should you use it?  Why should they be used and how?  Read on to discover the answers and more.

What is a Hyper-V snapshot?

While it seems like a simple question, defining what a Hyper-V snapshot is can be problematic. One of the most important things is not to confuse a Volume Shadow Copy Service (VSS) snapshot with a Hyper-V snapshot. While both can be used to restore a virtual machine (VM) to a prior state, they work in fundamentally different ways. VSS operates on the block level of the file system and only backs up disk information, while a Hyper-V snapshot captures disk and memory information of a VM by creating a separate automatic Virtual Hard Disk (.AVHD) file to track changes.

When, why, and how should they be used?

A Hyper-V snapshot should be used when applying patches, software updates, or reconfiguration of software. If something goes wrong or does not function as expected, you can revert back to the snapshot and undo all that was done. This allows you to go back in time and get the VM functional without having to do a restore from backup. Unlike VSS snapshots, Hyper-V snapshots aren’t the answer to backups or disaster recovery. Instead, you should use them as a troubleshooting option, should a configuration change or patch update cause problems. They are a great tool for a quick revert to a previous state, much as you would use the system restore option on your PC.

If you create many snapshots or let snapshots exist longer than necessary, VM performance could be affected or worse.  The differencing disk files are tracking changes made to the drives.  The more changes that occur, the larger the files become.  Let it run too long on snapshots and you can consume all the available space on the host’s drive and cause the guest(s) to crash.

Helpful tips:

  • Delete your snapshots as soon as possible to commit current changes to the VM.
  • Take your snapshot with the VM powered down so you do not have to use additional disk space when taking a snapshot of a running VM’s memory.
  • Do not rely on snapshots as a method of backing up your VM

Hyper-V snapshots can be an invaluable tool to revert from unexpected issues after patching or other OS changes.  If you need more information or help setting up your Hyper-V snapshot process, contact us at info@peters.com or 630.832.0075.