On Thu, 14 Jun 2001, NetBSD Bob wrote:

> > So an "mt -f /dev/mt0 retension" doesn not work on the TK series
> > drives?
>
> Nope.  AFIK, in the sources the retension and erase commands are
> specifically not operational.  I even checked some old PDP11 ultrix
> sources, and same there, too.
>
> To me, that suggests the hardware does not support retension or erase,
> in the traditional sense of the old 9 track reels or 1/4 inch streamer
> cartridges.  That must be not a bug but a feature!
>
> I have this nagging habit of wanting to retension all tapes before use,
> and erase all tapes before an initial write.  Old habits die hard.
> The TK50 transports just don't do that well.
>
> >  Is there maybe a mechanical way to forward the tape (I am
> > thinking maybe hacking an old broken TK50 drive to just have it spin the
> > tape to the end, and then maybe stick it into a decent drive and let it
> > rewind??
>
> I don't know of a way to manually do it, although I did get a powered
> up TK50 not on any interface to spin and roll the tapes, as a test.
> It rolled it about half way out of the cartridge, at high speed, but
> did not finish the retension.  Pressing the load button rewound it, OK.
> That helps a little, but is not a best solution.

I don't know how to get around the retension, but you could probably use
the following to erase the tape.

  dd if=/dev/zero of=/dev/rmt0 bs=64k

I don't know if 64k is the optimal block size or not, but I read a message
a few days ago on the list suggesting 64k as a good read size for the
TK50.

-brian.