HSG80 ACS Solution Software V8.6 for IBM AIM Installation and Configuration Guide

Planning a Subsystem 1–17
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.
It is recommended to use the following conventions 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.
Selective Storage Presentation
Selective Storage presentation is a feature of the HSG80 controller that enables the user to
control the allocation of storage space and shared access to storage across multiple hosts.
This is also known as Restricting Host Access.
In a subsystem that is attached to more than one host or if the hosts have more than one
adapter, it is possible to reserve certain units for the exclusive use of certain host
connections.
For a controller pair, the method used to restrict host access depends on whether the
controllers are in transparent or multiple-bus failover mode. For a single controller, the
methods are the same as for a controller pair in transparent failover.
Table 1–1 Unit Assignments and SCSI_VERSION
SCSI_VERSION Offset Unit Assignment What the connection sees LUN 0 as
SCSI-2 Divisible by 10 At offsets Unit whose number matches offset
SCSI-3 Divisible by 10 Not at offsets CCL