Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!decwrl!fernwood!portal!cup.portal.com!rwm
From: rwm@cup.portal.com (Richard DARYL Millett)
Newsgroups: comp.periphs.scsi
Subject: Re: SCSI LUNs
Message-ID: <41167@cup.portal.com>
Date: 11 Apr 91 17:05:58 GMT
Organization: The Portal System (TM)
Lines: 44


>Can anyone out there help on a point of interest ? I seem to recall that
>someone on this network mentioned the fact that with SCSI-2 you could
>achieve 256 LUN devices on one SCSI address by using the extended message
>format. I have looked through my copy of the SCSI-2 specification and have
>found no reference to extended messages and LUNs. How is this achieved ?
>And is it just an 'adaptation' of SCSI ?
>
>                Thanks,
>                        Dave Hollingsworth.


The reference that I have found that relates to this is in the SCSI 1 manual
X3.131-1986.  It reads as follows:
           ---------------------------------------------


Table 5-7 EXTENDED IDENTIFY
=================================================================
Byte |  Value | Description                                     |
=================================================================
 0   |  01h   | Extended Message                                |
-----------------------------------------------------------------
 1   |  02h   | Extended Message Length                         |
-----------------------------------------------------------------
 2   |  03h   | Extended Identify Code                          |
-----------------------------------------------------------------
 3   |   x    | Sub-logical unit number                         |
 ----------------------------------------------------------------

        The EXTENDED IDENTIFY message (Table 5-7) is optional and may be sent
by a target or an initiator.  It may be used in conjunction with the normal
IDENTIFY message in order to expand the logical unit number addressing in a
target.  The sub-logical unit number specifies the encoded eight-bit
sub-logical unit number used to identify on of 256 sub-logical units within
the logical unit.  This allows up to 2048 units to be addressed on a single
target.

                --------------------------------------

Richard Millett
Pioneer Communications
(408) 988-1702
usenet: rwm@cup.portal.com