[Bug-ddrescue] Doesn't seek when reading from tape.

[Grzegorz Nowakowski]

Hi.

Recently I was trying to recover data from old DDS tape and was hoping
ddrescue would help me.  While the program is quite useful, I stumbled
upon unexpected behaviour (say, undocumented feature?), that is, it
doesn't position tape before reading.  To clarify, I'll describe the
scenario:

1. start from position 0;
2. ddrescue reads the tape and writes to a file;
3. there is tape reading error, after some retries system reports error
  to application;
3a. if uninterrupted, ddrescue will try to read further, marking further
   locations as erroneous, while in truth the drive stops and doesn't read
   anything, just reporting read errors;
4. to reset drive, tape must be rewound;
5. after tape is repositioned at 0 and ddrescue is restarted with log
  file, it will append new data at the end of output file, but it will
  read it from the beginning of the tape;

I don't feel if there is good solution to the issue stated in point 3a.
It might be drive dependent, software handler dependend, and so on.  But
what happens at point 5, whether intentional or not, defies the
ddrescue's magic.  Right now, when hardware reports error, I need to
check tape position or calculate it from logfile, so I know where was
last good data (3a) and then manually rewind tape and feed ddrescue with
ipos and outpos arguments so it does put the data in order.  My point is
that without the second isse, ddrescue could be used in fire-and-forget
mode, with the only problem being too big areas marked as bad (split or
not), which would be eventually filled.  But as for today, it provides
just a little more functionality than that provided by old dd.

The version of ddrescue which I'm referring to is 1.2.

Best regards.
-- 
Grzegorz Nowakowski