logical unit number

A logical unit number (LUN) is a unique identifier used on a SCSI bus that enables it to differentiate between up to eight separate devices (each of which is a logical unit). Each LUN is a unique number that identifies a specific logical unit, which may be an end user, a file, or an application program.

A SCSI (Small System Computer Interface) is a parallel interface, that can have up to eight devices all attached through a single cable; the cable and the host (computer) adapter make up the SCSI bus. The bus allows the interchange of information between devices independently of the host. In the SCSI program, each device is assigned a unique number, which is either a number between 0 and 7 for an 8-bit (narrow) bus, or between 8 and 16 for a 16-bit (wide) bus. The devices that request input/output (I/O) operations are initiators and the devices that perform these operations are targets. Each target has the capacity to connect up to eight additional devices through its own controller; these devices are the logical units, each of which is assigned a unique number for identification to the SCSI controller for command processing.

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More resources from around the web: - SearchStorage.com provides links to more information about SCSA and LUNs. - PC Magazine includes a story, "SCSI Just Keeps On Rolling: Targets and LUNs."

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