[Fibre Channel] An FC_Port that contains functions associated with the Arbitrated Loop topology.


[Data Recovery] An identifier associated with a removable media or cartridge.

Labels may be humanly readable, machine readable, or both. See external volume serial number, media ID.

laboratory attack

[Data Security] Use of sophisticated signal recovery equipment in a laboratory environment to recover information from data storage media. [NIST SP 800-88]

Magnetic force microscopes and other similar equipment can be used to recover data from magnetic media that has been erased or damaged.


[Network] Acronym for Local Area Network.


[Network] Acronym for Local Area Network Emulation.


[Fibre Channel] One of multiple point-to-point physical connections that make up a single link.

LAN-free backup

[Data Recovery] A backup methodology that moves data over a SAN without using LAN resources.

large read request
large write request
large I/O request

[Storage System] An I/O request that specifies the transfer of a large amount of data.

‘Large’ depends on the context, but typically refers to requests for 64 KBytes or more of data. See small I/O request.


[Network] In the context of serial data communication networks, a solid-state element that emits light, usually in the near-infrared or infrared spectrum, modulated to carry binary information at very high data rates along an optical fiber.

The term laser was originally an acronym for "light amplification by stimulated emission of radiation.”


1. [Computer System] Synonym for I/O request execution time, the time between the making of an I/O request and completion of the request’s execution.

2. [Computer System] Short for rotational latency, the time between the completion of a seek and the instant of arrival of the first block of data to be transferred at the disk’s read/write head.

latent fault

[Computer System] A failure of a system component that has not been recognized because the failed aspect of the component has not been exercised since the occurrence of the failure.

A field-developed media defect on a disk surface is a latent fault until an attempt is made to read the data in a block that spans the defect.


[Storage System] Acronym for Logical Block Address.


[Network] An optical fiber connector complying with international standard IEC 61754-20:2002.

LC connectors are the most common connector in optical data communications networks, including Ethernet and Fibre Channel. A dual LC connector is used, carrying separate fibers for transmitted and received data.


[Network] Acronym for Lightweight Directory Access Protocol.


[Storage System] Acronym for Logical Disk Manager.

least privilege

[Data Security] The security objective of granting users only those accesses they need to perform their official duties. [NIST SP 800-12]


[Computer System] Acronym for Light Emitting Diode.

legal hold

[Legal] Process of suspending the normal disposition or processing of records and Electronically Stored Information as a result of current or anticipated litigation, audit, government investigation or other such matters. [ISO/IEC 27050-1]

The issued communication that implements the legal hold can also be called a "hold," “preservation order,” “suspension order,” “freeze notice,” “hold order,” or “hold notice.”


[Storage System] A storage device containing a robotic media handler capable of storing multiple pieces of removable media and loading and unloading them from one or more drives in arbitrary order.

lifecycle deletion

[Storage System] The deletion of data at the end of its lifecycle.

See disposition policy.

Light Emitting Diode (LED)

[Computer System] A multimode light source based on inexpensive optical diodes.

Available in a variety of wavelengths; 1300 nanometer wavelength is typical for data communications. The practical transfer rate limit for LEDs is 266 Mbps.

Lightweight Directory Access Protocol (LDAP)

[Network] An IETF protocol—originally a subset of the X.500 protocol—for creating, accessing and removing objects and data from a directory.

LDAP provides the ability to search, compare, add, delete and modify directory objects, as well as modifying the names of these objects. It also supports bind, unbind and abandon (cancel) operations for a session. LDAP got its name from its goal of being a simpler form of DAP (Directory Access Protocol).

Linear Tape File System (LTFS)

1. [File System] A self-describing, self-contained tape storage format intended for interchange of data between different software systems.

See ISO/IEC 20919.

2. [File System] A software or hardware implementation of a file system using the LTFS tape format.

Linear Tape Open (LTO)

[Tape] An open standard magnetic tape technology developed in cooperation by HP, IBM and Quantum.


1. [General] A physical connection (electrical or optical) between two nodes of a network.

2. [Fibre Channel] Two unidirectional fibers or conductors transmitting in opposite directions and their associated transmitters and receivers.

3. [Fibre Channel] The full-duplex FC-0 level association between FC-1 entities in directly attached ports.

4. [Fibre Channel] The point to point physical connection from one element of a Fibre Channel fabric to the next.

5. [Fibre Channel] A collection of multiple lanes.


[Fibre Channel] Acronym for Loop Initialization Primitive.


[Fibre Channel] Acronym for Loop Initialization Select Master.

litigation hold

[Legal] Synonym for legal hold.

load balancing

[Computer System] The adjustment of system and/or application components and data so that application I/O or computational demands are spread as evenly as possible across a system's physical resources.

I/O load balancing may be done manually (by a human) or automatically (by some means that does not require human intervention). See load optimization, load sharing.

load optimization

[Computer System] The manipulation of an I/O load in such a way that performance is optimal by some objective metric.

Load optimization may be achieved by load balancing across several components, or by other means, such as request reordering or interleaved execution. See load balancing, load sharing.

load sharing

[Storage System] The division of an I/O load or task among several storage subsystem components, without any attempt to equalize each component’s share of the work.

See I/O load balancing, load optimization.

load/store architecture

[Computer System] A CPU architecture in which memory is only accessed through load and store instructions, and all other instructions access data in registers only.

load/store operations

[Computer System] Operations that move data between CPU registers and memory.

local area network

[Network] A communications infrastructure—typically Ethernet—designed to use dedicated wiring over a limited distance (typically a diameter of less than five kilometers) to connect a large number of intercommunicating nodes.

See wide area network.

Local Area Network Emulation (LANE)

[Network] A collection of protocols and services that combine to create an emulated local area network using ATM as the underlying network.

Local area network emulation enables intelligent devices with ATM connections to communicate with remote LAN-connected devices as if they were directly connected to the LAN.

local backup

[Data Recovery] A backup methodology that utilizes host resources to copy data to a backup location that is under control of the same host.

local F_Port

[Fibre Channel] The F_Port to which a particular N_Port is directly attached by a link.


[General] Any method of managing concurrent access to a resource.

logical block

[Storage System] A block of data stored on a disk or tape, and associated with an address for purposes of retrieval or overwriting.

The term logical block is typically used to refer to the host’s view of data addressing on a physical device. Within a storage device, there is often a further conversion between the logical blocks presented to hosts and the physical media locations at which the corresponding data is stored. See physical block, virtual block.

logical block address

[Storage System] The address of a logical block, i.e., the offset of the block from the beginning of the block address space of the logical device that contains it.

Logical block addresses are typically used in hosts’ I/O commands. The SCSI disk command protocol, for example, uses logical block addresses.

logical disk

[Storage System] A set of consecutively addressed disk blocks that is part of a single virtual disk to physical disk mapping.

Logical disks are used in some array implementations as constituents of logical volumes or partitions. Logical disks are normally not visible to the host environment, except during array configuration operations. See extent,virtual disk.

logical disk manager

[Windows] A name for the volume management control software in the Windows NT operating system.

Logical Unit (LU)

[SCSI] The addressable entity within a SCSI target that executes I/O commands.

Logical Unit Number (LUN)

1. [SCSI] The SCSI identifier of a logical unit within a target.

2. [SCSI] Industry shorthand, when phrased as "lun", for the logical unit indicated by the logical unit number.

logical volume

[Storage System] A virtual disk, also called a virtual disk, or volume set, made up of logical disks.

long wavelength laser

[Fibre Channel] A laser with a wavelength 1300 nm or longer; usually 1300 or 1550 nanometers; widely used in the telecommunications industry.

long-term data retention

[Data Management] The practice of archiving data for extended periods of time, including ‘forever’.

Issues related to security and media, application and display formats must all be addressed for successful long-term retention. See data preservation.

long-term preservation

[Long Term Retention] The act of maintaining information, in a correct and independently understandable form, over a period of decades or longer.

See digital preservation.

loop initialization

[Fibre Channel] The protocol by which a Fibre Channel Arbitrated Loop network initializes upon power up or recovers after a failure or other unexpected condition.

Loop Initialization Primitive (LIP)

[Fibre Channel] A Fibre Channel primitive used to (1) initiate a procedure that results in unique addressing for all nodes, (2) indicate a loop failure, or (3) reset a specific node.

During a LIP, the nodes present on the arbitrated loop identify themselves and acquire addresses on the loop for communication. No data can be transferred on an arbitrated loop until a LIP is complete.

Loop Initialization Select Master (LISM)

[Fibre Channel] The process by which a temporary Fibre Channel arbitrated loop master is determined during loop initialization.

loop port state machine

[Fibre Channel] Logic that monitors and performs the tasks required for initialization and access to a Fibre Channel arbitrated loop.

loop switch

[Fibre Channel] A Fibre Channel switch operating at the layer 2 level allowing multiple dynamic point-to-point connections between devices using the FC-AL protocol.

Loop switches do not implement the Fibre Channel Switch Fabric protocols (FC-SW-x standards).


[Fibre Channel] An FC-1 operational mode in which information passed to the FC-1 transmitter is shunted directly to the FC-1 receiver.

When a Fibre Channel interface is in loopback mode, the loopback signal overrides any external signal detected by the receiver.

lossless Ethernet bridging element

[Fibre Channel] [Network] An Ethernet bridging function supporting the minimum required capabilities of Lossless Ethernet MACs.

lossless Ethernet MAC

[Fibre Channel] [Network] A full duplex Ethernet MAC that supports at least 2.5KB jumbo frames and implements extensions to avoid Ethernet frame loss due to congestion (e.g., the Ethernet Pause mechanism).

lossless Ethernet network

[Fibre Channel] [Network] An Ethernet network composed only of full duplex links, Lossless Ethernet MACs, and Lossless Ethernet bridging elements.


[File System] Acronym for Linear Tape File System.

LTFS Index

[File System] Metadata which describes the file data types and locations on an LTFS volume.

LTFS Volume

[File System] A tape cartridge utilizing the LTFS format.


[Storage System] Acronym for Linear Tape Open.


[SCSI] Acronym for Logical Unit.


[SCSI] Acronym for Logical Unit Number.


[Fibre Channel] Acronym for Long Wavelength Laser.