From owner-freebsd-current  Thu May  9 18:19:04 1996
Return-Path: owner-current
Received: (from root@localhost)
          by freefall.freebsd.org (8.7.3/8.7.3) id SAA24838
          for current-outgoing; Thu, 9 May 1996 18:19:04 -0700 (PDT)
Received: from ref.tfs.com (ref.tfs.com [140.145.254.251])
          by freefall.freebsd.org (8.7.3/8.7.3) with ESMTP id SAA24796
          for <current@FreeBSD.ORG>; Thu, 9 May 1996 18:18:58 -0700 (PDT)
Received: (from julian@localhost) by ref.tfs.com (8.7.3/8.6.9) id LAA25044; Thu, 9 May 1996 11:23:06 -0700 (PDT)
Message-Id: <199605091823.LAA25044@ref.tfs.com>
Subject: Re: more than 32 scsi disks on a single machine ?
To: jgreco@brasil.moneng.mei.com (Joe Greco)
Date: Thu, 9 May 1996 11:23:05 -0700 (PDT)
From: "JULIAN Elischer" <julian@ref.tfs.com>
Cc: bde@zeta.org.au, asami@cs.berkeley.edu, current@FreeBSD.ORG,
        nisha@cs.berkeley.edu
In-Reply-To: <199605091422.JAA00522@brasil.moneng.mei.com> from "Joe Greco" at May 9, 96 09:22:11 am
X-Mailer: ELM [version 2.4 PL25 ME8b]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-current@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

> 
> 
> > >Can we connect more than 32 disks on a single machine?  I tried
> > 
> > No.
> 
[...]
> > >#define	makedev(x,y)	((dev_t)(((x) << 8) | (y)))	/* create dev_t */
> > 
> > >So it seems like we're limited to 32 disks.
> > 
> > This limits us to 16777216 disks, or only 8388606 disks if we avoid using
> > the high bit to avoid sign extension bugs.  The limit is in dkunit() in
> > <sys/disklabel.h>
> > 
[...]
> > There are lots of things to change.  The encoding would have to be really
> > ugly to preserve compatibility with existing device nodes.
> 
> What if we don't give a damn about existing device nodes?  :-)  "Take the
> plunge".
[...]
> 
> 
> I understand how this device node scheme came to be.  I just happen to 
> think that however and whenever possible, we should work to remove such
> constraints.  :-)
> 

Peter Wemm and I have designed (and I have SOME code for)
a complete revamp of the disk system..
it is a total and complete rewrite, and will use a different 
(single) major-number/entrypoint for all disk type devices.
it will require devfs to be really useful, though it can be
hacked to work without it with preassigned numbers.