HP Surestore 660ex - Optical Jukebox, User Manual, Page: 99 / 130

Appendix B B-3
Operating This Jukebox on a SCSI Bus
A Brief Overview of SCSI
Op
eration o
n
a
SC
SI
Bu
s
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.
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).
8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7
Wide Address Range
Narrow
Addresses
Priority