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logical unit (LU)

The term Logical Unit (LU) is used in storage networks and in the SNA architecture.

  1. In storage area networks (SAN), a logical unit (LU) is an instance of SCSI that executes I/O commands. For example, an SCSI physical disk typically has one logical unit. Tape drives and array controllers can have multiple Logical Units that can be accessed via I/O commands. Logical Units are identified by the Logical Unit Number (LUN).

  2. In SNA networks, a logical unit is a logical virtual port that provides the user with access to network services. An LU supports at least two sessions: with the host-resident system service control point

    (SSCP) and with another LU representing, for example, an

    application program


    LUs are classified into types, with types LU 0, 1, 2, 3, 4, 5, and 7 communicating with host systems, peripheral devices

    , and applications, respectively.

    For example, LU 0 is for special devices and programs, LU 1 and LU 3 are for printers

    , and LU 2 is for 3270 series viewers with different screen sizes. LU 4 is similar to LU 1, but older, and LU 5 is undefined. LU

    7 is similar to LU 2, but is for sessions between the /36, /38, AS/400 and 5250 terminals

    . LU types 6.0, 6.1 and 6.2 can communicate with the same LU type. LU 6.2 is responsible for peer-to-peer communication in SNA networks. LU 6.2 supports general communication between programs in a distributed application environment, Advanced Program to Program Communication (APPC). With the definitions specified in the LU 6.2 protocol, it is also possible to communicate directly without FEP via the Cluster Controller. A prerequisite for the use of LU 6.2 is a PU 2.1 (Physical Unit).

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Englisch: logical unit - LU
Updated at: 17.09.2018
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