On Sun, 23 Jan 2000, Laine Stump wrote:

> make the question more generic by replacing "LUN" with something like
> "platter".

I think I know what you're talking about.  I remember reading about
autochangers like the one you describe a long time ago.  They pretended
that they were seven separate single-disc CD-ROM's and automatically
loaded whatever disk you accessed.

The ch-based players use a protocol that's part of the SCSI-2 command set
that describes robotic changers in general.  It has a notion of devices,
storage slots, and robotic arms, any of which can exist in quantities
greater than 1 for a single changer--it intends to be very general.  I
think Amanda can use it for tape robots.  The operating system is expected
to tell the changer where to go, on these new players.

In short, the old type of changer was a kludge to work around not having
SCSI-2 yet, and thus no ch specification; and also because it was probably
easier to write this firmware hack than to write a ch-ish driver for
MesS-DOS.  Most of the public/educational libraries who bought these
things when they first came out were probably using DOS.

The ``problem'' with the new way under NetBSD is that the ch and cd
drivers are separate and unaware of each other, so if you want to use CD
#2, then the isofs on CD #1 needs to be _unmounted_ before you can eject
and run the robot.  I'm not sure if amd could be convinced to deal with
this situation very well.  The Situation is arguably still the RT, but I
can see how it's less flexible in practice.

Maybe the dropping cost of hardware can be used as an excuse for giving
up:  single-disc CD players cost, what, $20-$40 these days, and hard disc
space approaching $0.01/MB means that enough space to hold an entire
CD-ROM will soon cost you about $6.50.

-- 
Miles Nordin / v:+1 720 841-8308 fax:+1 530 579-8680
555 Bryant Street PMB 182 / Palo Alto, CA 94301-1700 / US