These classnotes are depreciated. As of 2005, I no longer teach the classes. Notes will remain online for legacy purposes

UNIX02/Traditional UNIX Backup Tools

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Traditionally, UNIX systems have used a number of very simply, low-level commands for their backups. These days, most of the time you will probably wind up using commercial backup tools that are very well documented, or alternative open-source backup tools that are equally well documented. However, it does pay to see the core tools... the tools that most of these modern backup options utilize.

Selecting the backup tool

There are many tools that can be used to make backups. The traditional UNIX tools used for backups are tar, cpio, and dump. In addition, there are large number of third party packages (both freeware and commercial) that can be used. The choice of backup medium can affect the choice of tool.

tar and cpio are similar, and mostly equivalent from a backup point of view. Both are capable of storing files on tapes, and retrieving files from them. Both are capable of using almost any media, since the kernel device drivers take care of the low level device handling and the devices all tend to look alike to user level programs. Some UNIX versions of tar and cpio may have problems with unusual files (symbolic links, device files, files with very long pathnames, and so on), but the Linux versions should handle all files correctly.

dump is different in that it reads the filesystem directly and not via the filesystem. It is also written specifically for backups; tar and cpio are really for archiving files, although they work for backups as well.

Reading the filesystem directly has some advantages. It makes it possible to back files up without affecting their time stamps; for tar and cpio, you would have to mount the filesystem read-only first. Directly reading the filesystem is also more effective, if everything needs to be backed up, since it can be done with much less disk head movement. The major disadvantage is that it makes the backup program specific to one filesystem type; the Linux dump program understands the ext2 filesystem only.

dump also directly supports backup levels; with tar and cpio this has to be implemented with other tools.

See discussion in the SAG:

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Last edited May 17, 2003 7:34 pm (diff)
(C) Copyright 2003 Samuel Hart
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