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<H1><A NAME="SECTION001130000000000000000">Selecting the backup tool</A></H1>
<P>
There are many tools that can be used to make backups. The
traditional UNIX tools used for backups are <tt>tar</tt><A NAME="3020"> </A>,
<tt>cpio</tt><A NAME="3022"> </A>, and <tt>dump</tt><A NAME="3024"> </A>. 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.
<P>
<tt>tar</tt><A NAME="3026"> </A> and <tt>cpio</tt><A NAME="3028"> </A> 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 <tt>tar</tt><A NAME="3030"> </A> and <tt>cpio</tt><A NAME="3032"> </A> 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.
<P>
<tt>dump</tt><A NAME="3034"> </A> is different in that it reads the filesystem
directly and not via the filesystem. It is also written
specifically for backups; <tt>tar</tt><A NAME="3036"> </A> and <tt>cpio</tt><A NAME="3038"> </A> are
really for archiving files, although they work for backups
as well.
<P>
Reading the filesystem directly has some advantages. It makes
it possible to back files up without affecting their time
stamps; for <tt>tar</tt><A NAME="3040"> </A> and <tt>cpio</tt><A NAME="3042"> </A>, 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 <tt>dump</tt><A NAME="3044"> </A> program understands
the ext2 filesystem only.
<P>
<tt>dump</tt><A NAME="3046"> </A> also directly supports backup levels (which we'll
be discussing below); with <tt>tar</tt><A NAME="3048"> </A> and <tt>cpio</tt><A NAME="3050"> </A> this has
to be implemented with other tools.
<P>
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.
<P>
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<P><ADDRESS>
<I>Lars Wirzenius <BR>
Sat Nov 15 02:32:11 EET 1997</I>
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