Looking to read past EOT on DDS/DLT/LTO

Stan Sieler sieler at allegro.com
Fri Jan 27 17:41:14 CST 2017


Maciej mentioned "winding a tape past a medium error and read...".

I have several times successfully skipped past media errors on DDS-1
drives by doing a FSF (Forward Skip File ... tells drive to skip to the
next EOF).  (Although, IIRC, once I encountered a read error, I couldn't
do that ... I recall having to 'sneak up' on the error by positioning
the drive to the prior EOF and then skipping forward.  But since I haven't
done it for more than 10 year, maybe my memories are classic, er, rusty.)

My recollection is that DDS-1 (and perhaps -2?) had 'set marks' that
few people knew about, and even fewer ever used.  The explanation
I recall is that the drive could do a "forward to next setmark" *much*
faster than "forward to next EOF".  (BTW, when reading, a setmark
was reported like an EOF (although if you requested extra status you
could tell them apart).)

I never tried using the skip-to-next-setmark to get past errors,
partially because the tapes I was recovering years ago didn't have setmarks.

(Set marks are one reason I prefer my tape archiving format, since I record
as well as retry information :)

Al: thanks for expanding my answer about cutting out a portion of the tape
... I'd forgotten about helical recording.
(Note that on ordinary multi-track tapes, cutting a section
does indeed lose data from n different places on the tape ...
any tape that requires multiple passes over the tape to get from BOT to
the full capacity of the tape.)


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