HP storageworks HSG80 Reference Manual page 49

The unit number is the designation by which the controller keeps track of the unit.
This number maps to one or more host-accessible LUNs. Unit numbers are
prefixed by D and are in the range of 0–199. How units are assigned to ports
depends on the failover mode.
• Transparent failover mode:
— D0 to D99 are units assigned to port 1
— D100 to D199 are units assigned to port 2
— In transparent failover mode, adding unit D1 creates a logical unit and
NOTE: When a dual redundant pair of controllers is in Transparent Failover Mode,
only one port per controller is active.
• Multiple-bus failover mode:
— D0 to D199 are units visible to the hosts through both ports of both
— In multiple-bus failover mode, adding unit D0 creates a logical unit that is
Refer to the detailed description of failover modes that are contained in the
controller installation and configuration guide for further information regarding
the relationship between unit numbers and failover mode.
All units composed from the partitioning of a storage set must be maintained on
the same controller.
The LUN number a host connection uses to access a unit is a function of the
UNIT_OFFSET switch in the ADD (or SET) CONNECTIONS command. LUN
number equals unit number minus offset:
LUN number = unit number – offset
If no value is specified for the UNIT_OFFSET switch in the ADD (or SET)
CONNECTIONS command, the offsets are as follows:
• In transparent failover mode, host connections on port 1 have an offset of 0
and host connections on port 2 have an offset of 100.
• In multiple-bus failover mode, all ports have a default offset of 0.
HSG80 Array Controller V8.7 Command Line Interface Reference Guide
presents it as D1 to the host on port 1. Adding unit D101 creates a logical
unit and presents it as D1 to the host on port 2.
controllers
presented to both ports on both controllers. What hosts can see the unit is
determined by parameters of the ADD CONNECTIONS command and
by the ENABLE/DISABLE_ACCESS_PATH switch of the ADD UNITS
command.
ADD UNITS
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