HSG80 ACS Solution Software V8.6 for Compaq OpenVMS Installation and Configuration Guide

Planning a Subsystem 1–13
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: OpenVMS 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 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In this example, if a unit 20 is defined, it will be superseded by the CCL and invisible to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.
If SCSI_VERSION is set to SCSI-2 mode, the CCL floats, moving to the first available
LUN location, depending on the configuration.