[FAQ] Please read the FAQ [was: Re: Backup?!]

[Claus-Justus Heine <claus@momo.math.rwth-aachen.de>]

Hi Jo, at the end is an addition I'd like to see added to section

  3.6.  Why does my XYZ backup program complain about "Invalid argument"
  errors?

of the ftape FAQ. Thank you!

> I cannot get Tob to use the tape with afio. I even reinstalled tob after
> removing all my old configuration files which I used when I did backups to
> a second hard drive.  The tob error message reads : 
> 
> afio: "/dev/fape": Invalid argument. 

Here's the corresponding section of the Ftape-FAQ (FAQ == frequently
asked questions). Maybe the beta-5 and beta-6 versions of the FAQ
doesn't contain this answer, below is included the section of the FAQ
that Johan De Wit has put together (thanks, Jo!); it is available in
html format from the ftape web page

http://www-math.math.rwth-aachen.de/~LBFM/claus/ftape

in the "Documentation" subsection of that docuement. It is planned
that Jo places the html version of the FAQ on a web server he has
direct access to; until this has been made possible recent versions of
the FAQ are available from the Ftape Home Page as indicated above.

You can either read the html version on-line, or download the sgml
source from the web page.

Post 3.04-beta-6 versions will contain the text version of the most
recent FAQ at release time of the respective ftape version.

**********************************************************************
Please read the Faq. Thank you! If your problem isn't dealt with in
the FAQ then use the mailing list, if the answers given in the FAQ are
not clear enough, then please try to improve the FAQ. If you can't
correct the answers yourself, then please drop a short note to

the FAQ maintainer:

     Johan De Wit <jdewit@unicall.be>

the Ftape maintainer:

     Claus-Justus Heine <claus@momo.math.rwth-aachen.de>

the Linux tape mailing list:

     <linux-tape@vger.rutgers.edu>

stating that you found an answer to your question in the FAQ, but
couldn't understand what the hell people were talking about in that
answer.

If you feel that something is missing in the FAQ then please also
notify us using all of the addresses given above.

Other improvements (correction of typos etc.) are also welcome!

Please include the word FAQ in the subject line if you are sending an
email that is FAQ related, i.e. suggests improvements to the Ftape
FAQ.

Thank you.
**********************************************************************

Here you go:
------------------------------------------------------------------------
  3.6.  Why does my XYZ backup program complain about "Invalid argument"
  errors?

  zftape requires the data to be written in multiples of a fixed minimal
  block size. This is a very usual behavior for a tape device. There are
  three ways to get rid of those errors:

  o  set Ftape's block size to the block size used by the backup
     program. The example below works for "afio":

       mt -f /dev/qft0 setblk 5120

  o  If you don't want to use Ftape's built in compression you can also
     use

       mt -f /dev/qft0 setblk 0

  to switch Ftape to variable block size mode and be able to write the
  data in arbitrary portions to the tape (BUT: the builtin compression
  doesn't work with this setting). When you intend to use "KBackup" then
  this is the only way to make it work together with Ftape (it _may_
  work, don't know if it does)

  o  tell your backup program about Ftape's default block size of 10k
     (which is also the default of GNU tar). For "afio" you can use the
     following command line switch:

       afio -b 10k ...

  You may want to read the section "Tape blocks" of the manual (use its
  "Concept index" to directly jump to that section)

  <answer by Claus Heine>
------------------------------------------------------------------------

> "tar -czvf /dev/ftape *"  does not work but
> "tar -cvf /dev/ftape *" works.

Well, this isn't stated very clearly in the FAQ. We should add the
following to the answer given above.

########################################################################

When using GNU tar's builtin compression with GNU tar versions prior
to tar-1.12 one needs to run tar with the "--block-compress" switch to
"re-block" the output to the tape. Otherwise tar will compress the
data it reads and write it in arbitrary portions to the tape.
Example:

tar -czvf /dev/qft0 --block-compress /etc

WARNING:
One shouldn't use tar's builtin compression with large backups as it
makes the entire data stream one huge compressed block. If such
archives are corrupted right at the beginning it will be very
difficult to recover.

########################################################################


--
TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to
debian-user-request@lists.debian.org . 
Trouble?  e-mail to templin@bucknell.edu .