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Using Dump for Linux/Unix data backup

Dump is a standard utility for backing up file systems on Linux, Unix and BSD machines. It's free, powerful, fast and, in spite of its drawbacks, is widely used to back up *nix systems. Dump is losing some ground to third-party backup software, but because of its advantages many users prefer it. Here are some of the major advantages and disadvantages of using dump to back up your data.

Dump is free.

Nearly every version of Linux, Unix or BSD comes with dump; all of them are similar. There are enough differences that you need to study the documentation of your particular version before using it, but once you understand dump you pretty much understand it on all *nix systems.

Dump is time-tested.

Dump originally appeared in Unix Version 6 and has been used by administrators for file system backups for well over a decade. It is thoroughly tested and well-understood in the Unix/Linux/BSD communities.

Dump handles nine levels (or more) of incremental backups.

One of the best features of dump is its ability to do incremental backups. The original versions of dump could do nine levels of backups, and the latest versions can do even more. Dump's incremental backup lets you set up elaborate backup schedules with just a couple of switch settings and a simple script. For example, setting up a Tower of Hanoi backup scheme is easy with dump.

For more information on the Tower of Hanoi and other backup schemes, check out this related article

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on tape rotation strategies.

Dump is fast.

Because it is based on blocks, not files, dump is extremely fast.

However, dump also has some drawbacks, which is why it's losing ground in the *nix world to other backup utilities, including commercial products. Some disadvantages include:

Dump backs up file systems, not files.

Because it is block-based, dump isn't oriented toward files. It doesn't have a lot of fine control at the file or directory level. For backing up individual files, utilities like tar or cpio are better.

It doesn't work with all file systems.

Dump works with ext2/ext3 file systems. It doesn't support FAT, RieserFS or most other file systems. Needless to say it doesn't work with Windows either.

Dump is complex.

Dump is a classic example of a *nix utility. There are a lot of switches, not much explanation and dump assumes you mean what you tell it. It's powerful, but when used carelessly it can hopelessly corrupt your backups, or your entire file system.

It (mostly) can't handle files that change while the filesystem is being backed up.

Dump is not designed to back up active file systems and if a file changes during the process, the backup is likely to be corrupted. To use dump successfully you need to be sure that the file system is inactive, back it up when it is not being used or take a snapshot and back up from that. (Read-only file systems don't have a problem because they don't change.) It is also important to verify your backups.

A few variations of dump, such as xfsdump for the XFS file system can back up active file systems. However, this is not the norm.

If you decide to use dump, be sure to carefully study the way it works on your system. Although the dump utility is basically the same on all Unix/Linux/BSD versions, the differences among versions can be significant.

About the author: Rick Cook specializes in writing about issues related to storage and storage management.

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This was first published in November 2008

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