Recovering 4mm tar tapes

[Pete Turnbull]

On 12/09/2016 16:12, Douglas Taylor wrote:
> I have a pair of 4mm DDS tapes from 1999 that I would like to recover.
> I was able to read one with tar on a Debian (jessie) Linux system, but
> the second gives an error.

> The second tape is a 3M brand with DDS markings and 4 bars next to the
> DDS logo.  It also has 'Media Recognition System' and DD-90 written on
> it.  Here is the dialog and error:

> root at T5400deb:/home/taylor/4mm_tar_1998# tar -xvf /dev/st0
> tar: /dev/st0: Cannot read: Input/output error
> tar: At beginning of tape, quitting now
> tar: Error is not recoverable: exiting now

> (None of the config jumpers were installed for the tape that I could
> read)  Is the 2nd tape just bad and can't be read?  Or do I need a
> slightly different tape drive?

It could be corrupt, or it could be byte-swapped, or it could have a 
strange block size (especially a small one), or the heads might need 
cleaned after reading the last tape, or it might not have any valid 
data.  Does the debian tape driver support byte-swapping?  Or is there a 
bs and non-bs version?  You could try reading it with something like
  dd if=/dev/rmt/tapedevice bs=20b conv=swab | tar tvf -
or whatever the debian tape device equivalent is.  Does debian have some 
equivalent to mt(1) to read/set the drive's blocksize and to move 
forward and back along the tape?

Personally I hate DDS/DDS2/DDS3.  I always had better luck with half 
inch and even 8mm, and better still with DLT.

-- 
Pete
Pete Turnbull