HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning a Subsystem
1–18 HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
Figure 1–12: 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 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
1–21.
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