Specifications

3–13
Compaq HSG80 Array Controller ACS Version 8.4 Configuration and CLI Reference Guide
Assigning Unit Offsets
Unit offsets are used to define the first unit number that a host connection is able to
access on the controller. Many operating systems have a limited addressing range,
such as 0–7. Using unit offsets allows hosts to see controller LUNs at 0–7.
When assigning unit offsets, keep in mind that the unit offset is set on a host
connection basis. Thus, one host connection can have a unit offset of 0 and see units
0–99 as LUNs 0–99, and another host connection can have a unit offset of 10 and see
units 10–99 as LUNs 0–89 (controller unit number 10 is seen at the host as LUN 0).
This process is useful for hosts that have a limited LUN addressing range.
Figure 3–8 depicts the use of unit offsets on host connection basis. Note that
controller units 0–99 are presented only on port 1, and units 100–199 are presented
only on port 2. This implies that port 1 host connections can have a unit offset range
of 0–99, and port 2 host connections can have a unit offset range of 100–199.
Figure 3–8 LUN Presentation Using Unit Offset on a Per-Host Basis
Controller
Units
HOST 1
on Port 1
Dev Offset: 0
HOST 2
on Port 1
Dev Offset: 20
HOST 3
on Port 2
Dev Offset: 100
LUN 0
LUN 1
LUN 2
LUN 3
LUN 20
LUN 21
LUN 0
LUN 1
LUN 0
LUN 1
LUN 2
LUN 30
LUN 31
D0
D1
D2
D3
D20
D21
D100
D101
D102
D130
D131
CXO6455A