bill@unixland.uucp (Bill Heiser) (03/03/91)
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.)
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other: heiser@world.std.comdb@seachg.uucp (David Bell) (03/05/91)
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.) > > The SCSI spec allows up to 8 controllers on the bus, with SCSI id's from 0 to 7. Each controller may have up to four devices connected to it, with Logical Unit Numbers from 0 to 3. All devices that have built in SCSI controllers (such as the CDC Wren drives) have a LUN of 0. -- Dave Bell Sea Change Corporation Mississauga, Ontario, Canada UUCP: ...!uunet!attcan!seachg!db
gerry@zds-ux.UUCP (Gerry Gleason) (03/05/91)
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
neese@adaptx1.UUCP (03/05/91)
>/* ---------- "LUN on SCSI drives" ---------- */ >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.) The LUN (Logical Unit Number) is a subset of the controller ID. In SCSI you can have a total (currently) of 8 target ID's (0-7) on the SCSI bus. These target ID's are essentially the controllers/adapters on the bus. Attached to each target ID/controller you can have 8 LUN's (0-7). The LUN is set in the actual SCSI command sent to the target/controller. All in all you could have 56 devices on the SCSI bus (7 targets with 8 LUNS attached to each target = 56 (This assumes one adapter taking up one of the target ID slots)). Roy Neese Adaptec Senior SCSI Applications Engineer UUCP @ neese@adaptex
gerry@zds-ux.UUCP (Gerry Gleason) (03/07/91)
In article <1991Mar4.185942.1554@seachg.uucp> db@seachg.UUCP (David Bell) writes: >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 >The SCSI spec allows up to 8 controllers on the bus, with SCSI id's from 0 >to 7. Each controller may have up to four devices connected to it, with >Logical Unit Numbers from 0 to 3. Only partially correct. LUN is a 3 bit field, therefore 0-7 are possible. Also, there is provision for a sub-LUN, via an extended message which is 8 more bits. (Wait let me make sure) Yes, that's it. You send: 01h Extended message 02h Extended message length 02h EXTENDED IDENTIFY code XXh Sub-logical unit number Gerry Gleason
goykhman_a@apollo.HP.COM (Alex Goykhman) (03/08/91)
In article <283400064@adaptx1> neese@adaptx1.UUCP writes: > >>/* ---------- "LUN on SCSI drives" ---------- */ >>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.) > >The LUN (Logical Unit Number) is a subset of the controller ID. In SCSI >you can have a total (currently) of 8 target ID's (0-7) on the SCSI bus. >These target ID's are essentially the controllers/adapters on the bus. >Attached to each target ID/controller you can have 8 LUN's (0-7). The >LUN is set in the actual SCSI command sent to the target/controller. >All in all you could have 56 devices on the SCSI bus (7 targets with >8 LUNS attached to each target = 56 (This assumes one adapter taking up >one of the target ID slots)). SCSI allows up to 256 LUNs per target via an optional EXTENDED IDENTIFY message, though I am not aware of a single implementation that use it. SCSI-2 does not mention EXTENDED INTENTIFY at all, therefore is limited to 8 LUNs per target. > > Roy Neese > Adaptec Senior SCSI Applications Engineer > UUCP @ neese@adaptex ##############
RWM@cup.portal.com (Richard DARYL Millett) (03/15/91)
Actually according to the ANSI X3.131-1986 specifications you can actually have 2,048 peripheral devices per target using extended messages. That is a possibilty of 14,336 devices on 1 SCSI bus. (7*2048 = 14336) The Pioneer Optical drives support 4 LUNs per controller and I have heard of a company that actually put all 28 possible drives on a SCSI bus to see if it would work. Richard Millett Pioneer Communications rwm@cup.portal.com