Chapter 15 Backing Up Your Linux System 463

Floppy Disk: Good for making copies of your configuration files, such as /etc directory, because the size is very small and the disk can only hold 1.44MB. Not suitable for regular backups of your data.

Magnetic Cartridge: This type of magnetic media can hold from 100MB to 2GB of information on one cartridge. This is a good size media for use with small partitions, but not very useful in a larger environment.

CD-ROM: Can hold up to 600MB of information. Most often, CDs are used to archive data because of their durability and portability. For regular backups, however, CD-ROMs aren’t recommended.

Disk: This type simply copies your data to a different location (preferably another machine). Usually, the files are combined and compressed into an archive for easy retrieval. Disk backups, however, are susceptible to disk failures — just like regular data. Therefore, they are usually used in conjunction with tape backups. Disk backups can also take an enormous amount of space.

Tape: The most popular type of backup system. Tape drives come in a variety of sizes and media capacities. Magnetic tapes are reliable, can store a large amount of information, and can easily be transported to another location for protection in offsite storage. However, the drives must be constantly maintained through regular cleanings to remove buildup on the tape heads and to prevent tapes from being damaged.

Know the different types of backup methods, rotation schemes, and devices that can be used for backing up different types of files and systems.

Recovering data

Administrators commonly restore files from backup because users regularly delete files, and because files become corrupt or accidentally overridden. The most difficult task in restoring files is finding the media that holds the correct files. If the file was deleted, the administrator simply returns to the last backup before the deletion took place. If the file is corrupted, the administrator may have to search for a version of the file that doesn’t appear to be corrupted. When restoring files from your backup media to your system, keep in mind some general rules:

Never overwrite the original. If it still exists, never overwrite the original file with the restored file. If the owner has already added some work to that file, you may be deleting data that can’t be recovered. Always create a separate directory called “restore,” and restore the files to that directory. This way, users can compare the files and replace their data as needed.

Restore incremental and differential backups after a full backup. In the event that you are restoring a full file system, always restore your last full