Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!zds-ux!gerry
From: gerry@zds-ux.UUCP (Gerry Gleason)
Newsgroups: comp.periphs.scsi
Subject: Re: LUN on SCSI drives
Message-ID: <554@zds-ux.UUCP>
Date: 4 Mar 91 21:01:46 GMT
References: <1991Mar2.184349.1595@unixland.uucp>
Reply-To: gerry@zds-ux.UUCP (Gerry Gleason)
Organization: Zenith Data Systems
Lines: 23

In article <1991Mar2.184349.1595@unixland.uucp> bill@unixland.uucp (Bill Heiser) writes:
>I'm kind of confused about the "LUN" on SCSI drives...  For 
>example, when I look at my drive configuration using scsicntl,
>it shows both a SCSI id and a LUN for each unit.  I don't see
>any documentation referring to LUN anyplace though.  Is that
>something different from SCSI id?  How is it configured?  I don't
>see any reference to it, at least in my CDC Wren manual (I'm still
>waiting for Maxtor to send me the manual for the 8760S.)

LUN=Logical Unit Number, and it is different than SCSI ID.  The SCSI
ID aka Bus ID, is the address of a particular target controller, and
the LUN is used to identify each of more than one device at a particular
bus tap.  Since most of the drives that are out there have the target
controller integrated with the drive, each Bus ID typically only has on
logical unit (almost universally LUN 0), there is not much cause to
worry about LUN's.

I've only seen one device so far that has multiple LUN's.  Dennon CD-ROM
drives have can daisy chain up to four drives together on a proprietary
bus, with the SCSI cable going to one of them.  In this configuration,
each drive has the same bus-id, but a different LUN.

Gerry Gleason