djh@crosfield.co.uk (david hollingsworth) (04/10/91)
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.
rwm@cup.portal.com (Richard DARYL Millett) (04/12/91)
>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
jlohmeye@donald.WichitaKS.NCR.COM (John Lohmeyer) (04/15/91)
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