Difference between SCSI ID and logical unit number?

[Fred L. Johnson]

In article <HENKEL%NEPJT.91Jun24132655 at ners6k2.ncsuvx.ncsu.edu>,
henkel%nepjt at ncsuvx.ncsu.edu (Chuck Henkel) writes:

> A connection address for a SCSI device has the form AA-BB-CC-DD where
> DD, according to info, is the SCSI ID and logical unit number [LUN],
> in that order.
> 
> So what is the LUN? Is it always 0? The SCSI ID is set on the device
> itself; is the LUN also? 

The logical unit number is just a way to subdivide a SCSI ID so that several
devices in a single logical unit can be addressed by the same SCSI ID but
also can be addressed individually via the LUN.  It increases greatly the
number of devices that can be attached to a single SCSI bus.

Currently all of the supported devices have a single LUN which is set to 
zero.  I know of some OEMs that are working on multiple LUN devices for
the RISC System/6000 and I would imagine that we would release some of our
own.  The software support for multiple LUNs is already in place.

- Fred

My remarks and opinions are mine alone...
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