Robert Mazur <no-one@no-domain.com> wrote:
> Upon your suggestion, I tried accessing the tape using mt. As usual, I
> got an I/O error when trying /dev/rmt/0. I was not clear (still aren't)
> on what all the other symbolic links were in my /dev/rmt/
> directory....items like:
> 0, 0b, 0bn, 0c, 0cb, 0cbn, 0cn, 0h,.....etc.

The 'st' man page has all the answers. There's a density flag
(l|m|h|u|c) a BSD compatibility flag (b) and the selection of the
non-rewind device (n). I'd use 0cbn unless you had a reason not to.

> So I started trying mt -f /dev/rmt/<each_of_the_entries_above>

> When I got to /dev/rmt/0l, we had contact, and I could make full use of
> some tar commands.

What was the output on one of the devices that didn't work?

> I saw in a doc somewhere that using /dev/rmt/0n
> would prevent the tape from rewinding after the tape was written to.
> What is the meaning of all the other entries/links?

No. 0n leaves the tape in position after being written to (so you can
write something else afterward). 0 (no n) automatically rewinds the
tape after the first write is complete. That can cause problems if you
don't expect it.

> So, either the drive was working all along and I was trying to change
> /kernel/drv/st.conf a few dozen times for no reason, or maybe changes
> were required even before I stumbled on /dev/rmt/0l? I suspect the
> former, but some trial and error would let me know.

Not all drives make use of all the density flags. Some drives (like the
mammoth 8mm) treat them all identically. When they're used to
distinguish between different densities, l is the bottom. Think (l)ow,
(m)edium, (h)igh, and ((u)ltra high or (c)ompressed).

For instance the DLT7000 drive will write a tape in uncompressed DLT4000
compatibility mode (20GB capacity) when using the 'l' density. It will
write in compressed DLT7000 mode (~70GB capacity) when using the 'u' or
'c' density.

I would normally expect the 'c' device (usually as 'cbn') to be the
correct one. Some combinations of drive and media may not be valid for
all densities.

> For now, I have some backing up to do. Thanks for all the help guys.

Good luck.

--
Darren Dunham ddunham@taos.com
Senior Technical Consultant TAOS http://www.taos.com/
Got some Dr Pepper? San Francisco, CA bay area
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