12.3. 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
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
dump also directly supports
backup levels (which we'll be discussing below); with
tar and cpio this has to
be implemented with other tools.
A comparison of the third party backup tools is beyond
the scope of this book. The Linux Software Map lists many of
the freeware ones.