When managing a virtual machine, snapshots can be your friend. They can make some processes simpler, and offer a VM administrator a wider choice of options. Here is all you need to know about VM snapshots, and how you can use them.
VM snapshots have their uses, but are not a substitute for backups
What The Heck Is A VM Snapshot? First of all, let's begin with a definition. A virtual machine (VM) snapshot is a snapshot of a virtual machine's disk data, configuration, and overall state at a particular moment in time. A VM snapshot can be taken while the virtual machine is running, and you can take multiple snapshots as well.
VM snapshots provide a change log for the virtual disk, and can be used to restore a virtual machine to the point when the snapshot was taken. Not to be confused with a backup, the VM snapshot simply rolls a virtual machine back and restores local data that may have been lost due to corruption or just simple data loss.
VM Backup Versus VM Snapshot A VM backup doesn't rely on the original data disk format. It creates a duplicate copy of the data that can then be stored offsite safely for later use. Backups are thorough. A VM snapshot is an image of the virtual machine as it was during a fixed point in time, a read-only picture.
As a rule VM snapshots are stored on-site, which makes them vulnerable if something happens to the location in question, like, say, a fire or power loss.
VM snapshots should never be considered a substitute for a backup.
What's A Snapshot Good For? Snapshots are best used for software developers and testers, training purposes, and technical support services. The VM snapshot facilitates recreating different computer environments as well as particular conditions within said environments.
You can restore a virtual machine to the exact point when the snapshot was taken, even to the point of overwriting the old data, or even merge the current data with the snapshot itself.
Snapshot Downside The article "Snapshots: A Love-Hate Relationship for VM snapshot" points out that snapshots have their drawbacks, eating away at the capacities of the data store as well as the basic hard drive files. According to the article, "A Delta-file can grow to be as large as the data file, meaning a 40 GB basic hard drive file can create Delta hard drives amounting to another 40 GB per snapshot."
That's why if you are going to use VM snapshot, you have to be particularly careful when monitoring data usage, and the number of snapshots that are accumulating.
Conclusion What needs to be remembered here is that the VM snapshot is a poor man's backup, but can provide a quick easy means of resetting a virtual machine in order to bring it back to a particular point. It has its place in the IT department, but should never take the place of a full backup.