Compaq HSZ80 manual Assigning Unit Numbers for Host Access to Storagesets, 32Creating Storagesets

3–32Creating Storagesets

Assigning Unit Numbers for Host Access to

Storagesets

The HSZ80 controller supports up to 15 SCSI target IDs, each of which can present up to 32 logical unit numbers (LUNs) to a host, depending on the requirements of your operating system. However, a maximum number of 128 storage units can be presented to a host by a controller or a dual-redundant pair of controllers. One of these is reserved for the StorageWorks Command Console (SWCC) interface, which leaves 127 available for use.

You will need to assign a unique unit number to each storageset, single disk unit, or storage device that you want your host to know about in your subsystem. A unit number is an alphanumeric name that identifies each storage unit in your subsystem, such as D102 for a disk-based storage unit. The host uses these names 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: use D for disk drives or P for passthrough devices such as tape drives, loaders, and libraries.

■A first number that indicates which controller accesses the storage unit during normal operation. Use one of the controller’s SCSI target IDs: 0 to 15.

By carefully choosing the first number, you can establish preferred paths for all of your storage units in a dual-redundant configuration.

■A second number that is always zero.

■A third number that identifies the LUN for the device or storage unit (0 to 7).