It's 9 in the evening. Do you know if your backups work? Do you know when you last made a successful backup of all of your data? Do you know whether you can restore from that backup? If not, how well can you sleep?

You should verify your backups, and do it regularly, not just when you first set up the backup system. Verification means doing whatever you need to do to ensure all of your precious data has been backed up and can be correctly restored from the backups.

The simplest way to do that is to restore all your data, and compare it with your live data, and note any differences. That requires you have enough free disk space to restore everything, but it's the almost the only way to be really sure.

It's also a great way to ensure the restoring actually works. If you don't test that, don't be sure you can do it when needed.

Some backup software has a verification mode, which doesn't actually write the restored data to disk, but compares it with live data directly. This can save space, and can be a reasonable compromise, but you should test actual restoring as well. You could do that by restoring only some of the live data, perhaps choosing files randomly for each test.

If you have the disk space to do a complete restore, doing so is a great way to excercise your disaster recovery process in general. Here's one way of doing it:

  • On your main computer, do a backup.
  • On a second computer, perhaps borrowed for this, restore all your data, without using your main computer at all.
  • Start using the restored data as your live data. Do real work, and do all the things you normally do. Pretend your main computer was eaten by your pet shark.
  • If you notice something missing, or being corrupt, or being too old, get the files from your main computer, and fix your backup process so that the next time you won't have that problem.

How often should you do that? That, again, depends on how you feel about your data, and how much you trust your backup tools and processes. If it's really important that you can recover from a disaster, you need to verify more frequently. If data loss is merely inconvenient and not life-changingly disastrous, you can verify less often.