Looking to read past EOT on DDS/DLT/LTO - test-drb@ccmp.vtda.org

26 Jan 2017

Hi,
Thanks for the notes/comments/suggestions.
Recovery service: not that I've found.  Most of the ones I know of have *us*
as their HP 3000 experts (i.e., we help them :) ... when I've asked in
recent years
about handling damaged or overwritten DDS (or newer) tapes, I've always been told
'no'.
The "cut out some tape" would definitely not work.  At least LTO, probably DLT,
have multiple tracks and the tape makes multiple passes from start of tape to end of
tape as it writes the entire tape.  That means on a 16 track tape, you'd lose part
of 16 different sections if you cut out a piece of tape (ignoring the question of whether
or not the drive could resynch after such an error :)
Eric's reply is closest to home ... that's why I mentioned a 'hacked'
drive,
hoping someone might know specialists who have one.
Chuck mentioned an approach I had mentioned: the power kill during writing approach.
I'm hesitant to try that as it will (based on dim memory of doing it 15 years ago
on a DDS) lose a small bit of data ... if it works at all.
I'm giving up for now.
thanks,
Stan
...
  From: Eric Smith <spacewar at gmail.com>
 I hope someone can prove me wrong, but I think that short of a major effort
 to hack the drive firmware, the data is gone. Modern tape drives are "too
 smart" to allow reading past logical EOT, and the tape format is too
 complex to allow fooling the firmware by any simple means.
 ------------------------------
 From: "Nico de Jong" <nico at farumdata.dk>
 I've had the same problem some years back, with a DDS-3, IIRC
 I did some research, and the most reasonable outcome was that it was not
 possible by normal means, because some algorithm reading synchronisation
 data couldnt find out what was happening, so, the backup was ruined.....
 ---- 
...
  From: Chuck Guzis <cclist at sydex.com>
 With nothing left to lose, I suppose that one might overwrite the EOT
 and then kill power during the write, then attempt to read backward from
 the end of the tape.
 ------------------------------
 From: "js at cimmeri.com" <js at cimmeri.com>
 Would it be possible to just physically
 cut the 1kb + EOT portion of tape out,
 and then attempt to read from
 beginning?  I suppose this would depend
 on how the backup data is formatted on
 the tape (using some kind of container
 format with error checking, for instance).
 ------------------------------
 From: Jerry Weiss <jsw at ieee.org>
 Have you approached a commercial recovery service for a quote?
 A few do tape media.   Whether they quote or not may provide a data point about how
feasible it may be. ----