How do I read a bad tape (tar)?

[Jeremy Higdon]

In article <1991Apr10.004953.17211 at leland.Stanford.EDU>, dhinds at elaine19.Stanford.EDU (David Hinds) writes:
> In article <1991Apr9.225311.6534 at lokkur.dexter.mi.us> scs at lokkur.dexter.mi.us (Steve Simmons) writes:
> >olson at anchor.esd.sgi.com (Dave Olson) writes:
> >
> >Hmmm...some help might be possible here.  First, one needs to trick
> >the drive into reading past the EOT (not EOD) marker.  This *can* be
> >done with some drives (I've done it), as long as one is careful.  An
> >EOT marker is two tape marks.  So *if* the conjecture about a small
> >tar blotzing the head of a large one is true, one could do so by doing
> >
> >   mt -f <no_rewind_tape> fsf 1 ; mt -f <no_rewind_tape> fsf 1
> >
> >Now the tape is positioned past the EOT mark.  Use GNU tar to read the
> >damaged data.
> 
>     I didn't realize you could just step past the tape marks like this.

You can do this with a half-inch tape, or sometimes, with an Exabyte.
The original poster had a cartridge tape, so I doubt that the above
will work.

> What I've done before, to get past an EOD, is to rewrite another small
> archive over the one causing the problem, but then eject the tape from
> the drive before it writes its EOD.  Then, reading the tape runs into
> a media error, but hopefully tar should try to resynchronize and read
> the rest of the tape.
> 
>  -David Hinds
>   dhinds at cb-iris.stanford.edu