Chapter 19. Backing Up Your Data

When all else fails . . . restore from backup!

Keeping good backups is frequently the only way to recover from some accidents, disasters, or break-ins. Linux has a number of methods for archiving your data, ranging from tools like tar or cpio that come with Linux to feature-rich, sophisticated, commercial packages.

There are a number of ways to keep backups, ranging from simply taring your entire filesystem to a tape to using dump and a well-designed backup schedule to running high-end commercial backup and restore programs.

Of course, you also have a variety of backup media to choose from: floppies (if you are truly desperate), tape drives (from old nine tracks up to DAT), write once, read many (WORM) drives, magneto-optical floppies (written magnetically, read optically), and ZIP and JAZ drives. Of these, only the newer tape options and JAZ drives have gigabyte capacity, and only exabyte and DAT can handle more than a couple of gigabytes. Unfortunately, tapes are in many ways the most cumbersome to work with because of their sequential access nature.

With the new proposed standards for CD-ROM- (and thus WORM-) based filesystems, this media will soon sport multiple gigabyte capacity. Though they will still be write once, the easier access (random instead of sequential) will likely make them popular once their price drops into the affordable range. In actuality, the technology for this has existed for some time, but the popularity of the current standard has kept it from being replaced. However, the need to store large amounts of data reliably has grown tremendously in recent years, and CD-ROMs are a big win over tape in both ease of access and longevity (decades versus years).

The rest of this chapter assumes you have some form of large capacity media on which to back up your data, though many of the guidelines are useful regardless of the media being used or its capacity.

In general, you will want to run your backup during times of low activity for two reasons. One, it is not a good idea to have lots of files open or changing while the backup is running. Some programs will lock a file and the backup will, at best, be able to skip it, or, at worst, the backup will exit or crash. Second, backing up your system will tend to consume a lot of system resources, and if your server is fairly loaded already, it will likely be bogged down considerably if you try to run the backup during "normal" business hours (whatever those might be).