Glossary

logical port address

In a director or switch, the address used to specify port connectivity parameters and to assign link addresses for the attached channels and control units.

logical switch number

LSN. A two-digit number used by the I/O configuration program (IOCP) to identify a director or switch (D).

logical unit number

LUN. In Fibre Channel addressing, a logical unit number is a number assigned to a storage device which, in combination with the storage device’s node port’s world-wide name, represents a unique identifier for a logical device on a storage area network. Peripherals use LUNs to represent addresses. A small computer system interface (SCSI) device’s address can have up to eight LUNs.

login server

Entity within the Fibre Channel fabric that receives and responds to login requests.

longwave

Lasers or light-emitting diodes (LEDs) that emit light with wavelengths around 1300 nm. When using single mode (9 nm) fiber, longwave lasers can be used to achieve lengths greater than 2 Km.

loopback plug

In a fiber optic environment, a type of duplex connector used to wrap the optical output signal of a device directly to the optical input. Contrast with protective plug. Synonymous with wrap plug.

loopback test

Test that checks attachment or control unit circuitry, without checking the mechanism itself, by returning the output of the mechanism as input.

LPAR

See logical partition.

LSN

See logical switch number.

LUN

See logical unit number.