Tape overwritten

[Terry McGonigal]

In <1991Jan25.045736.12356 at tkou02.enet.dec.com>
diamond at jit345.swstokyo.dec.com (Norman Diamond) writes:

> In article <1991Jan24.213649.2804 at cc.ic.ac.uk> pjc at cc.ic.ac.uk writes:
> 
> >   TK50 that has had the front of a tar file overwritten by another
> >   much shorter one. Can I get at any of the data of the original file
> >   on the tape?
> >   I am willing to consider manually winding on the TK50 If I have to.
> >   MT seems unable to get past the EOF and the first partial block on
> >   the tape.
> 
> The default device used by the mt command is likely to rewind after
> obeying your instructions, so you might not know if it has gotten past
> the EOF.  Try:
> 
[ suggestions omitted ]

My experiences with this problem would suggest that it's not software
EOF marks that are the trouble here, but rather a hardware EOT mark that
the TKxx driver writes to the tape when it's finished writing to it.

Some poking around in man pages and .h's lead me to beleive that there is
a command you can give the drive to both write and erase these marks, but
I could'nt fingure out how to get the commands through the ioctl interface.
It does not, however seem to be possible to get the drive to space past
or over one of these marks, the drive `thinks' the tape ends there and gives
only i/o errors (I think, it's been a while) if you try to move past it.

We eventualy hit upon the idea of powering off the system (a GPX/II) during
a tar, which did work, leaving us with a tape w/o the EOT mark that gets
written when tar finishes (normally :), but this hardly seems like a sane
solution.  As it is a potentially common problem, I too would be interested
in any less drastic solutions...

> 
> These are not the company's suggestions.
> --
> Norman Diamond       diamond at tkov50.enet.dec.com
> If this were the company's opinion, I wouldn't be allowed to post it.
> 

Cheers,
-- 
Terry McGonigal    GeoVision Corp   {uunet,cunews!cognos}!geovision!terry
                   Ottawa On, Can   tmcgonigal at gvc.com
                   613-722-9518