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

Planning a Subsystem
1–13HSG80 ACS Solution Software Version 8.7 for Compaq OpenVMS Installation and
Configuration Guide
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.
IMPORTANT: 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In this example, if a unit 20 is defined, it will be superseded by the CCL and invisible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.
StorageWorks recommends to use the following conventions when assigning host
connection offsets and unit numbers in SCSI-2 mode: