Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!uunet!ncrcom!ncrwic!mickey!donald!jlohmeye From: jlohmeye@donald.WichitaKS.NCR.COM (John Lohmeyer) Newsgroups: comp.periphs.scsi Subject: Re: SCSI LUNs Message-ID: <500@donald.WichitaKS.NCR.COM> Date: 15 Apr 91 14:37:18 GMT References: <9419@suns7.crosfield.co.uk> Reply-To: jlohmeye@donald.WichitaKS.NCR.COM (John Lohmeyer) Organization: NCR Corporation Wichita, KS Lines: 25 In article <9419@suns7.crosfield.co.uk> djh@crosfield.co.uk (david hollingsworth) writes: >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 ? EXTENDED IDENTIFY message was removed from SCSI-2 because it was poorly documented and few people were actually using it. In its place, stream identifiers were added to the communications command set. (Okay, this is not a complete replacement.) SCSI-3 will extend the logical unit space from 8 to 32 logical units by using the 2 reserved bits in the IDENTIFY message. This also means that the LUN field in the CDB will be reserved and/or used for other functions in SCSI-3. SCSI-3 Packetized Protocol (for Fibre Channel and other packet interfaces) will extend the logical unit space even further (256, I think). -- John Lohmeyer John.Lohmeyer@WichitaKS.NCR.COM NCR Corp. uunet!ncrlnk!ncrwic!donald!jlohmeye 3718 N. Rock Rd. Voice: 316-636-8703 Wichita, KS 67226 SCSI BBS 316-636-8700 300/1200/2400 24 hours