SUMMARY: undo mt eof (?)

From: Need Help <unixtipzz_at_yahoo.com>
Date: Mon, 10 Sep 2001 06:15:59 -0700 (PDT)

thanks to Greg Poole, Dr. T Blinn and Jim for their
suggestions.
tapex encountered eof just immediately....so couldn't
recover the stuff on tape, luckily i had it tarred
somewhere else.
Does switch eom work with tru64? (end of media)?
i think the substitute is seod then.
Thanks all, responses follow.



--- "Dr. Thomas.Blinn_at_Compaq.com"
<tpb_at_doctor.zk3.dec.com> wrote:
>
> You have presumably written two tape marks (or
> perhaps only one)
> at the beginning of the tape. Use the "tapex"
> utility (found in
> the /usr/field directory, installed in the System
> Exercisers kit
> component, which is optional) to verify that there
> is still any
> data on the tape beyond the first tapemark. Then
> use "mt" to
> position past the tapemark you wrote. You can't
> recover any of
> the data that was overwritten, but you may be able
> to retrieve
> useful stuff beyond there.
>
> Remember that you must use the "no rewind" tape
> names with "mt"
> or you will just get the tape rewound after
> positioning, which
> is not useful if you're trying to get to data in a
> file beyond
> the beginning of the tape.
>
> Tom
>
> Dr. Thomas P. Blinn + UNIX Software Group + Compaq

         "Greg Poole" <gkpoole_at_tecoenergy.com> Book
     
I can't help with getting the data back, but the way
to get to the end
of the last save set is:
mt seod (set end of device)

I have never heard of anyone recovering from this or
even trying on
DLT.

On 8mm and DAT tape drives, you can over-write the EOT
that you
accidentally
wrote. This can be done without writing another EOT
by turning off the
tape drive or unplugging the SCSI bus before
dismounting the drive
or before 'close'-ing the output file.
The data you write could be garbage or could be
arranged to look like a
tar file or some other format you can read or skip
over.

I have no idea if this works on DLT.
DLT is physically quite different since it is
'serpentine'. I.e. tape
is
written several tracks in parallel forward to the
physical end of tape,
then the head is offset and more tracks are written
backward, then
offset again
and more written forward, etc. until the whole width
of the tape is
used.

On 8mm and DAT, some experimentation is necesasry to
write the correct
amount to overwrite the EOT but not damage anything
more than the first
file. (of course the first file is already destroyed
by your first
mistake).

To read the tape, you would then skip over the garbage
and read the
next file.

Jim Belonis

P.S. If you find this works, or find claims that it
works on the web
somewhere,
     Please publicize it.

ORIGINAL Question:
> > i wanted to move tape to end of current data,
> instead
> > did mt -f /dev/tape01 eof
> > so this marked the beginning of tape as the end,
> and
> > now can't read any of the info in it!!!!
> > Any undo this damage???
> > thanks
> > tru64 4.0f, dltiv tapes on tl89
> > need this info bad
> >
> > otherwise, what is perfect way to append data at
> end
> > of current data?
> > thanks

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Received on Mon Sep 10 2001 - 13:16:47 NZST

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