HP StorageWorks HSG80 ACS Solution Software V8.8 for Windows NT, Windows 2000, and Windows Server 2003 (32-bit) Installation and Configuration Guide (AA-RV1XA-TE, March 2005)

Planning a Subsystem
49HSG80 ACS Solution Software V8.8 for Windows NT, Windows 2000, and Windows Server
2003 (32-bit) Installation and Configuration Guide
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” on page 52.
Matching Units to Host Connections in Multiple-Bus Failover Mode
In multiple-bus failover mode, the ADD UNIT command creates a unit for host
connections to access. All unit numbers (0 through 199) are potentially visible on
all four controller ports, but are accessible only to those host connections for
which access path is enabled and which have offsets in the unit's range.
The LUN number a host connection assigns to a unit is a function of the
UNIT_OFFSET switch of the ADD
(or SET) CONNECTIONS command. The
default offset is 0. 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 (number the host sees the unit as)
— Unit number is relative to the controller (number the controller sees the
unit as)
For example, unit D7 would be visible to a host connection with an offset of 0 as
LUN 7 (unit number of 7 minus offset of 0). Unit D17 would be visible to a host
connection with an offset of 10 as LUN 7 (unit number of 17 minus offset of 10).
The unit would not be visible at all to a host connection with a unit offset of 18 or
greater, because that offset is not within the units range (unit number of 17 minus
offset of 18 is a negative number).
In addition, the access path to the host connection must be enabled for the
connection to access the unit. This is done through the ENABLE_ACCESS_PATH
switch of the ADD UNIT (or SET unit) command.