Using snapshots

One of the great features of Virtualbox (and most other hypervisors) is the ability to use snapshots. Snapshots enable you to create a point-in-time copy of the virtual machine state. For example, prior to performing an upgrade step or change (on any VM, not just this one), taking a snapshot enables you to go back to the moment prior to the snapshot creation. It is a really valuable tool that is worth learning how to use.

The snapshot management tools in Virtualbox can be found under the ‘Machine tools’ section on the right-hand side of the application. To create a point-in-time snapshot, use the Take button. To go back to that state is as simple as using the restore function.

If needed, it’s possible to have a tree of snapshots and go back to any one of them. Be aware, however, that each snapshot will cause a very slight degredation in performance. Therefore it’s good practice that snapshots are only used when appropriate and that they are regularly pruned (deleted) so that the performance doesn’t degrade.

The reason for this is that each snapshot essentially creates a new ‘delta’ disk: it makes the original disk read-only and stores only blocklevel changes between files – known as delta changes – at the point of each new snapshot. If a file changes often between snapshots, this can mean it has to be read multiple times from each one.