Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning a Subsystem 1–19
Assigning Unit Numbers and Host Connections 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 are recommendations 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In this example, if a unit 20 is defined, it will be superseded by the CCL and invisible to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 Unit Numbers and Host Connections 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. The following conventions are
recommended when assigning host connection offsets and unit numbers in SCSI-2 mode:
■ Offsets should be divisible by 10 (for consistency and simplicity).
■ Unit numbers should be assigned at connection offsets (so that every host connection
has a unit presented at LUN 0).
Table 1–1 summarizes the recommendations for unit assignments based on the
SCSI_VERSION switch.