Subject: Re: config question
To: None <firstname.lastname@example.org>
From: der Mouse <mouse@Collatz.McRCIM.McGill.EDU>
Date: 02/02/1995 06:44:02
> Under the 1.0 config(.new), on the SPARC, at least, one cannot attach
> sd/st/sr devices directly to the scsibus. [...]
> It would be much nicer to be able to declare
> esp* at sbus0 slot ? offset ?
> sd0 at esp0 target 0 drive 0
> instead of having to declare a "tg" target for each one.
> I'm just curious as to what rationale, if any, lies behind the way
> this works.
Of course I can't know, since I wasn't responsible for it, but I would
guess that this is because SCSI really has that logical extra level in
there: a SCSI bus fans out to (up to) seven[%] target ID numbers, each
of which has (up to) 8 (I think) units, which are the real devices.
[%] Not eight because one is used by the controller.
SunOS does what you asked for, by overloading the "drive" number to
specify both target ID and unit number at the same time. In my opinion
this is an ugly kludge, and I was glad to see NetBSD doing it right.
Before anyone hauls out the old "does anyone use LUNs?" I'll mention
that I own a Sun-3 that has two disks, and they're on target 0 unit 0
and target 0 unit 1.