Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning a Subsystem 1–17
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).
An additional factor to consider when assigning unit numbers and offsets is SCSI version.
If the SCSI_VERSION switch of the SET this_controller/other_controller command is set
to SCSI-3, the Command Console LUN (CCL) is presented as LUN 0 to every connection,
superseding any unit assignments. The interaction between SCSI version and unit
numbers is explained further in the next section.
In addition, the access path to the host connection must be enabled for the connection to
access the unit. See “Restricting Host Access in Transparent Failover Mode,” page 1–20.
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