Specifications

3–10 Controller and Host Addressing
Mapping the Containers and Storagesets to
the Host with Logical Units
In a subsystem, the host communicates to the physical devices through host-
addressable logical units, also called units. These units are created and given a logical
unit number (LUN) after adding physical devices, adding containers, and initializing
the containers. The host uses these numbers to indicate the source or target for every
I/O request it sends to a controller.
Each unit number contains the following:
■ A letter that indicates the kind of devices in the storage unit. For example, D for
disk drives.
■ A number from 0–199, depending on which failover mode you use.
IMPORTANT: For OpenVMS hosts, you must set a unit identifier just after
creating the logical unit. Without a unit identifier, the OpenVMS host will
never recognize the logical unit. For information on when to add the
identifier, see Chapter 6, “Configuring Storagesets.” For information on
the IDENTIFIER switch, see “SET controller,” page 7–91.
Assigning Unit Numbers in Transparent
Failover Mode
Each controller has two ports, port 1 and port 2, as shown in Figure 3–6. A set number
of units are accessible, depending on the host operating system.
In transparent failover mode, the range of assignable units is 0–99 on port 1, and 100-
199 on port 2, regardless of what unit offset is set on the host. Do not split partitioned
storagesets across ports; they must be on the same port.
See “ADD UNIT,” page 7–27 for more details.