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
50 HSG80 ACS Solution Software V8.8 for Windows NT, Windows 2000, and Windows Server
2003 (32-bit) Installation and Configuration Guide
The PREFERRED_PATH switch of the ADD UNIT (or SET unit) command
determines which controller of a dual-redundant pair initially accesses the unit.
Initially, PREFERRED_PATH determines which controller presents the unit as
Ready. The other controller presents the unit as Not Ready. Hosts can issue a SCSI
Start Unit command to move the unit from one controller to the other.
Assigning Unit Numbers Depending on SCSI_VERSION
The SCSI_VERSION switch of the SET
THIS_CONTROLLER/OTHER_CONTROLLER command determines how the
CCL is presented. There are two choices: SCSI-2 and SCSI-3. The choice for
SCSI_VERSION affects how certain unit numbers and certain host connection
offsets interact.
Assigning Host Connection Offsets and Unit Numbers in SCSI-3 Mode
If SCSI_VERSION is set to SCSI-3, the CCL is presented as LUN 0 to all
connections. The CCL supersedes any other unit assignment. Therefore, in
SCSI-3 mode, a unit that would normally be presented to a connection as LUN 0
is not visible to that connection at all.
The following methods are recommended for assigning host connection offsets
and unit numbers in SCSI-3 mode:
■ Offsets should be divisible by 10 (for consistency and simplicity).
■ Unit numbers should not be assigned at connection offsets (to avoid being
masked by the CCL at LUN 0).
For example, if a host connection has an offset of 20 and SCSI-3 mode is selected,
the connection will see LUNs as follows:
LUN 0 - CCL
LUN 1 - unit 21
LUN 2 - unit 22, etc.
In this example, if a unit 20 is defined, it will be superseded by the CCL and
invisible to the connection.
Assigning Host Connection Offsets and Unit Numbers in SCSI-2 Mode
Some operating systems expect or require a disk unit to be at LUN 0. In this case,
it is necessary to specify SCSI-2 mode.