We have a tar tape (no compression) that a second person started to
write over.

chdev blocksize was 10420.

The second tar was quickly stopped, but we need to get at the data
from the first tar.

HELP!

Haven't tried this before but maybe you can use TAR Repair (free trial)
http://www.tar-repair.com/

<fondue.meat@comcast.net> writes:

> We have a tar tape (no compression) that a second person started to
> write over.
>
> chdev blocksize was 10420.

Probably typo, as 10240 is much more likely value.

> The second tar was quickly stopped, but we need to get at the data
> from the first tar.

TAR format itself is actually very easy to recover -- you just

dd if=corrupt.tar bs=10240 skip=1 | tar tvf -

You may need to skip more than 1 block, but eventually you'll
skip past the EOF marker and will begin to see the files that are
still there.

[I am quite surprised that there is a commercial tar-repair company,
but I might be missing something, or maybe there are enough clueless
admins to support their existence].

You major problem is likely going to be extracting the data from
tape: when the second tar was interrupted, it likely wrote double
EOT marker, and getting the tape drive to read past what it considers
end-of-tape may be tricky.

Last time I needed to do that (on SCO Unix, IIRC), I couldn't get the
data off the tape no matter what I tried; the 'mt' driver simply
refused to read past the EOT.

You may have better luck on AIX though.

Cheers,
--
In order to understand recursion you must first understand recursion.
Remove /-nsp/ for email.