HP StorageWorks HSG80 ACS Solution Software V8.8 for Linux X86 Installation and Configuration Guide (AA-RV1LA-TE, March 2005)

Planning a Subsystem
44 HSG80 ACS Solution Software V8.8 for Linux X86 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", page 46.
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.
Note: Linux requires the controllers be set to SCSI-3 mode.
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 sees 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In this example, if a unit 20 is defined, it is superseded by the CCL and invisible to
the connection.