SCSI Element Addressing
Every logical library starts at the first drive slot with the current assigned element
start address (default value 256). It will be incremented from the bottom to the top
slots for every drive slot. There is one exception to this addressing scheme to
accommodate libraries currently in the field. A 4U library which contains only full
height drives will continue to have the addresses assignments 256 and 257, thus
causing no interruptions to their operation. Drive slots will still be incremented by

1 for each drive slot position.

Note: Exchanging drives with different form factors will result in the library

needing to be reconfigured.
The SCSI specification does not allow gaps in the SCSI element addressing. Special
handling is needed for empty drive slots to fulfill the specification. Also drives
which are temporarily removed need to have their address preserved to not
confuse the attached host and host application. Generally only drives are reported
which are currently physically available or temporarily removed. Empty (unused)
slots which are located at the bottom or the top should not be reported, with an
exception in case of a “removed” condition. A drive slot which does not contain a
drive and has a position between used slots needs to be reported as a SCSI
element. To signal the host application that this slot is not usable, its ACCESS bit
will be disabled.
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Drive3
256
ElementAddress
Drive2
256
ElementAddress
Drive1
256
ElementAddress
Magazine
1
Magazine
2
Magazine
3
Magazine
4
Frontside
Drive4
256
ElementAddress

Figure A-4. Configuration of a Four Partition System

SCSIElement Slot
4
3
2
1
SCSIElement Slot
4
3
2
1
257
256
257
256
258
4UUnit with only FH drives
(1logical library)
4UUnit with FH and HH drives
(1logical library)
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Figure A-5. Examples of SCSI Element Addressing

Appendix A. SCSI Element Types and Addresses A-5