HSG80 ACS Solution Software V8.6 for IBM AIM Installation and Configuration Guide

Planning a Subsystem 1–15
If no value is specified for offset, then connections on port 1 have a default offset of 0 and
connections on port 2 have a default offset of 100.
For example, if all host connections use the default offset values, unit D2 will be presented
to a port 1 host connection as LUN 2 (unit number of 2 minus offset of 0). Unit D102 will
be presented to a port 2 host connection as LUN 2 (unit number of D102 minus offset of
100).
Figure 1–10 shows how units are presented as different LUNs, depending on the offset of
the host. In this illustration, host connection 1 and host connection 2 would need to be on
host port 1; host connection 3 would need to be on host port 2.
Figure 1–10. LUN presentation to hosts, as determined by offset
Offsets other than the default values can be specified. For example, unit D17 would be
visible to a host connection on port 1 that had an offset of 10 as LUN 7 (unit number of 17
minus offset of 10). The unit would not be visible to a host connection with a unit offset of
18 or greater, because that offset is not within the unit’s range (unit number of 17 minus
offset of 18 is a negative number).
Similarly, unit D127 would be visible to a host connection on port 2 that had an offset of
120 as LUN 7 (unit number of 127 minus offset of 120). The unit would not be visible to a
host connection with a unit offset of 128 or greater, because that offset is not within the
unit’s range (unit number of 127 minus offset of 128 is a negative number).
Controller
units
Host
connection 1
Offset: 0
Host
connection 2
Offset: 20
Host
connection 3
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
CXO6455B