Mac® Security Bible

8.6. Managing Backup Media

In this chapter, I focus on backup methods that use hard disks as the storage medium. But whether you use disks, tapes, or optical discs, the same basic rules apply to handling and storing your backup media. Even the most thorough, diligent backups are worthless if the media on which they're stored is lost or damaged.

8.6.1. Offsite backups

The first rule of managing your backup media is to have at least two copies of all your data and to keep those copies in different places. One reason for keeping multiple backups is that any particular disk or tape can fail randomly, but it's much less likely that two or more backups would fail at the same time. But keeping all your backups in one location is like keeping all your eggs in one basket. If your home burns down or your office is burglarized and all your backups are right there near your computer, they'll all be gone, and you'll be out of luck. Therefore, common sense dictates that one of your copies should be kept somewhere else — preferably someplace reasonably far from the source.

One way to achieve this end — multiple copies, with at least one offsite — is to make two or more physical copies of everything and move one of them to another spot on a regular schedule (such as once a week). In the case of a Time Machine backup or a bootable duplicate, this could mean using one backup hard drive for a week and then unplugging it, plugging in a different one that you'll use for the following week, taking ...