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

Planning a Subsystem
1–17HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
1–17
•The UNIT_OFFSET switch in the ADD CONNECTIONS (or SET connections) commands
• The controller port to which the connection is attached
•The SCSI_VERSION switch of the SET THIS_CONTROLLER/OTHER_CONTROLLER command
The considerations for assigning unit numbers are discussed in the following sections.
Matching Units to Host Connections in Transparent Failover
Mode
In transparent failover mode, the ADD UNIT command creates a unit for host connection
to access and assigns it to either port 1 or port 2 of both controllers.
Unit numbers are assigned to ports as follows:
•0−99 are assigned to host port 1 of both controllers.
•100−199 are assigned to host port 2 of both controllers.
For example, unit D2 is on port 1, and unit D102 is available through port 2.
The LUN number that a host connection assigns to a unit is a function of the
UNIT_OFFSET switch of the
ADD (or SET) CONNECTIONS command. The relationship of
offset, LUN number, and unit number is shown in the following equation:
LUN number = unit number – offset
Where...
— LUN number is relative to the host (what the host sees the unit as)
— Unit number is relative to the controller (what the controller sees the unit as)
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 1–12 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.