This section describes some simple uses of tar and mt.
You can use `tar', `dd', `cpio', and
`afio'. You will need to use `mt' to get the full
potential of your tapes and the ftape driver. For a start
I'd recommend using `tar', as it can archive lots of
directories and let you pick out separate files from an archive.
cpio creates smaller archives and is more generally more
flexible than tar, but is missing some features like volume
labels. `afio' creates backups where each file is compressed
individually and then concatenated. This will allow you to access the
files ``after'' the point of the error. If you use gzipped
tar files, all data after the point of the error is lost! (to
me, this is a pretty good reason for NOT using compression on
backups). The choice of which is most appropriate depends on the
situation and the features and malfeatures of each of the packages. I
recommend taking a look at each package at reviewing the options that
each provides. It's possible that this HOWTO may provide more detail
on this subject at some point in the future.
To make a backup of your kernel source tree using tar, do this
(assuming you have the sources in /usr/src/linux):
cd /usr/src
tar cf /dev/ftape linux
This will not compress the files, but gives you a smoother tape run.
If you want the compression (and you've got tar 1.11.2), you
just include the -z flag(*), eg: `tar czf /dev/ftape
linux'
For further instructions on how to use tar, dd and
mt look at the man pages and the texinfo files that comes
with the respective distributions.
(*) tar assumes that the first argument is options, so the
`-' is not necessary, i.e. these two commands are the same:
`tar xzf /dev/ftape' and `tar -xzf /dev/ftape'
OK, let us restore the backup of the kernel source you made in section Writing an archive to a tape above. To do this you simply say
tar xf /dev/ftape
If you used compression, you will have to say
tar xzf /dev/ftape
When you use compression, gzip will complain about trailing
garbage after the very end of the archive (and this will lead to a
`broken pipe' message). This can be safely ignored.
For the other utilities, please read the man page.
tar has an option (-d) for detecting differences between two
archives. To test your backup of the kernel source say
tar df /dev/ftape
If you do not have the man page for tar, you are not lost
(yet); tar has a built-in option list: try `tar --help 2>&1 |
more'
tar file on a tapeTo put more than one tar file on a tape you must have the
mt utility. You will probably have it already, if you got one
of the mainline distributions, e.g.\ Slackware or Debian.
tar generates a single Tape ARchive (that's why it is called
`tar') and knows nothing about multiple files or positioning
of a tape, it just reads or writes from/to a device. mt knows
everything about moving the tape back and forth, but nothing about
reading the data off the tape. As you might have guessed,
tar and mt in conjunction, does the trick.
By using the nrft[0-3] (nftape) device, you can use
`mt' to position the tape the correct place (`mt -f
/dev/nftape fsf 2' means step over two ``file marks'', i.e.\
tar files) and then use tar to read or write the
relevant data.
``Is there a way to extend an archive -- put a file on the tape, then later, add more to the tape?''
No. The tar documentation will tell you to use `tar
-Ar', but it does not work. This is a limitation of the current
ftape driver.
Since a tape does not have a ``filesystem'' on it, you do not mount /
unmount the tape. To backup, you just insert the tape and run your
`tar' command (or whatever you use to access the tape with).