HELP! Bad 8mm tape!

[Herb Peyerl]

raj at pollux.geog.ucsb.edu (Richard A Johnson) writes:
>their files.  That's when I found that the tape had a bad spot!  If you
>manually advance the tape a little you find a place where it's crinkled a
>little bit.  When the drive gets to that part it stops reading and returns
>an error ("The media surface is damaged").

When was the last time you cleaned this drive??? I once had a drive totally
mangle a tape beyond repair, that's when I learnt to clean the drive
about every 30 hours of use... Haven't had a problem since then... We've
been using exabyte drives since '87 to back up our Apollo network... We
use 4 of them every night and back up about 1.6 GB on each. Also, ever
since we switched from the Sony VIDEO tapes to the actual REAL Exabyte
tapes, we've never had another soft media failure... With the sony's,
we were getting about 1 bad tape every month...

>IOCTL, etc. which will tell the drive not to rewind the tape.  Maybe there's
>a dip switch on the drive itself?

I know there isn't one on the drives WE get which are manufactured by
Exabyte.... It's likely your drives are manufactured by the same company.

>The ONLY thing I can think of would be to take the tape apart, cut off the bad
>part at the beginning, reattach the rest to the tapeup spool, and use dd to

I've never tried this so I can only speculate that it won't work... The
data is written onto the tape in much the same way as video information is
written to the tape... ie:

 ------------------------
  \  \  \  \  \  \  \  \ 
    \  \  \  \  \  \  \  \
  ------------------------

So, I'm fairly certain that if you cut a chunk out, the smarts in the
Exabyte drive itself would still detect an error and rewind... 

>I was trying to read some of my incremental saves.  One tape in particular
>read just fine the first 4 or so times and then started giving the same type
>of problem!  Now I doubt that the tape got mangled while it was still in the

It's happened to me, I don't doubt it's just happened to you.  'Specially
if you haven't cleaned it... I'm not an expert, but 4 drives for 4 years
adds up to a fair chunk of experience. Buy the 12 cycle cleaning kits from
Exabyte.  I know all their stuff is expensive, but how much is your data
worth anyways?

>a bad part of an 8mm tape?  It seems impossible!  You can bet I'm going to
>re-read ALL saves to 8mm tape in the future!  (I know, I should have
>this time...)

I've never lost ANY data by re-reading the data I knew I was about to 
destroy...  Sometimes a second copy is not entirely out of the question.
Also, reading all the backup logs every morning helps out.
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