We often hear from people that have lost their data, despite having some sort of backup. It’s important to remember that your backup is no-longer a backup if it becomes the only copy of your data. We usually suggest having at least two forms of backup to cover this problem.
We recently revisited this topic.
An example of a failed backup strategy came recently. A user had one server, and at the end of every day would duplicate the whole server to another server. This is OK for some scenarios and gives you a day-old server ready to bring out if your main server fails. We would have also suggested a second backup routine to run at the same time to some other storage. Preferably an external drive, accessible from a standard computer.
The system worked fine for over a year, until server 1 failed one day. Instead of replacing the disks and then restoring from the backup, it was decided to reuse the original disks and then load them from the backup. They overwrote server 1 with the backup from server 2.
When the restore was complete, it was discovered that the data on server 2 was actually corrupt. This corrupt data had also been written back to server 1. The client ended up with two corrupt servers, and no good copies of the data. Worst case scenario.
You will often hear that deleted data isn’t really deleted. This is kind of true, but only until you overwrite the data with something else. By writing server 2’s data over server 1, that effectively overwrote the original data, and left no possible avenues of recovery.
Another common problem we see is with external RAID cases like the Netgear ReadyNAS. These can be setup in a mirror mode which keeps the same data on both disks. Theoretically when one disk fails, the other can still be accessed. In reality the failed NAS will often end up in an unusable state where access to the data is not possible anyway. Even if you plug the hard drive directly into a PC, the NAS drives use a non-standard format so the data is not accessible.
The best way to avoid getting caught out by your backups is to never trust them. Be more paranoid. If you think you have a solid backup system then add another backup, just in case. Then next year add another. Most of the time it will seem irrelevant, but when your server and backup drives all get struck by lightning or end up flooded under six feet of water, you’ll be glad you spent the extra few pounds on an extra backup.
If you’re already using a Time Machine backup on your Mac then why not supplement that with a monthly whole-disk copy to a different drive. Carbon Copy Cloner or SuperDuper! can take care of it. This also has the advantage of being instantly bootable in an emergency and can even be stored in a locked safe, or at a friends’s house.