Recovering cartridge tape files

Recovering cartridge tape files

Post by Chuck Muscia » Sat, 08 Jun 1991 23:37:34



     I have a QIC-24 cartridge tape that had a number of files on it, and
then had another file written to the tape at the beginning.  This overwrote
at least one of the files on the tape, of course, but should not have harmed
the remaining files after that point.

     How can I recover the remaining files on the tape?  I tried using mt
and dd to move past EOT and continue reading, but had no luck.  Is there
some magic sequence of tape ioctl's I can use to skip the first file on
the tape and then continue reading subsequent files?

     I am using a QIC-24 SCSI tape drive on a Sun 3/280 running SunOS 4.0.3.

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Recovering cartridge tape files

Post by Braham Le » Wed, 12 Jun 1991 19:09:17



>      I have a QIC-24 cartridge tape that had a number of files on it, and
> then had another file written to the tape at the beginning.  This overwrote
> at least one of the files on the tape, of course, but should not have harmed
> the remaining files after that point.

>      How can I recover the remaining files on the tape?  I tried using mt
> and dd to move past EOT and continue reading, but had no luck.  Is there
> some magic sequence of tape ioctl's I can use to skip the first file on
> the tape and then continue reading subsequent files?

>      I am using a QIC-24 SCSI tape drive on a Sun 3/280 running SunOS 4.0.3.

if it can be done you'll need to use the non-rewind tape device. usually
this is the same device name but with a digit number higher eg /dev/mt0
and /dev/mt8, see man mt and associated for details on your system. dd
is probably the only way you'll get the stuff off, if you can at all.
the easiest thing to do then is to read the tape with dd twice. if you
want to be clever you can use `mt fsf` command but this mightn't work.
Quote:> --

braham

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1. erasing last file on cartridge tape

I have a little script that does basically this:

for var in a b c d e f g; do
        tar cf /dev/rmt/0bn dir-$var
done

Now, occasionally the tape will get full, e.g. at step 'e' in the
above step. So the tape is ejected, and a new tape is put in, and
step 'e' is restarted.

That's all fine. But I'd like to make the script a little smarter, i.e.
I'd like it to remove the incomplete data written to the first tape in
the first attempt of step 'e' from the full tape.

My idea is: at the point where tar returns an error (generally meaning
that the tape is full) the script will "mt bsf" some number of times so that
the next write would overwrite the 'e' step. Then I could "mt eof". Then
there should be two eof's in a row at that point on the tape, preventing
someone from reading the incomplete 'e' step. Right?

Now here's my question. Supposing I do this. What happens if I then do
"mt eom" on the 1st tape? Will I be able to write a smaller dataset to
the tape?

I'm going to experiment myself a bit, but of course it will be time-consuming,
so any hints anyone could give may save me some time.

Thanks!

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