Lun Addressing - HP Surestore 160ex - Optical Jukebox User Manual

Operating This Jukebox on a SCSI Bus
A Brief Overview of SCSI
an ID greater than 7, would always assume it won the contention and would attempt
to talk, perhaps at the same time as a device with an ID above 7 that was contending
for the bus. The following diagram shows the priority scale of IDs when the priority
of the two blocks of eight are reversed.
Priority
8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7
Narrow
Addresses
Wide Address Range
The diagram below shows the linear addressing of a simple, narrow bus with the
host adapter set at a SCSI ID of 7. The device ID does not determine where the
device is physically placed on the bus.

LUN Addressing

SCSI IDs are the top-level method of addressing devices on the bus. Another
method of addressing is also available; logical unit numbering (LUN). This method
enables a complex device, such as a jukebox, to group its internal SCSI devices to a
single SCSI ID.
The complex device is identified by a SCSI ID, but this complex device assigns
logical unit numbers (LUNs) to each device within it. Up to eight LUNs may be
assigned under a single SCSI ID. The LUNs that can be assigned are from 0 to 7
(LUN 0 is usually retained by the complex device).
Appendix B B-3