Specifications

For S/390 or zSeries hosts, a logical subsystem
represents a logical control unit (LCU). Each control-unit
image is associated with only one logical subsystem.
See control-unit image.
logical unit. The open-systems term for a logical disk
drive.
logical unit number (LUN). A SCSI term for a unique
number used on a SCSI bus to enable it to differentiate
between up to eight separate devices, each of which is
a logical unit.
logical volume. The storage medium associated with
a logical disk drive. A logical volume typically resides on
one or more storage devices. The ESS administrator
defines this unit of storage. The logical volume, when
residing on a RAID-5 array, is spread over 6 +P or 7 +P
drives, where P is parity. A logical volume can also
reside on a non-RAID storage device. See count key
data and fixed block address.
logical volume manager (LVM). A set of system
commands, library routines, and other tools that allow
the user to establish and control logical volume storage.
The LVM maps data between the logical view of storage
space and the physical disk drive module (DDM).
longitudinal redundancy check (LRC). A method of
error-checking during data transfer that involves
checking parity on a row of binary digits that are
members of a set that forms a matrix. Longitudinal
redundancy check is also called a longitudinal parity
check.
longwave laser adapter. A connector used between
host and the ESS to support longwave fibre-channel
communication.
loop. The physical connection between a pair of
device adapters in the ESS. See device adapter.
LPAR. See logical partition.
LRC. See longitudinal redundancy check.
LRU. See least recently used.
LSS. See logical subsystem.
LUN. See logical unit number.
LVM. See logical volume manager.
M
machine level control (MLC). A database that
contains the EC level and configuration of products in
the field.
machine reported product data (MRPD). Product
data gathered by a machine and sent to a destination
such as an IBM support server or RETAIN. These
records might include such information as feature code
information and product logical configuration
information.
mainframe. A computer, usually in a computer center,
with extensive capabilities and resources to which other
computers may be connected so that they can share
facilities. (T)
maintenance analysis procedure (MAP). A hardware
maintenance document that gives an IBM service
representative a step-by-step procedure for tracing a
symptom to the cause of a failure.
management information base (MIB). (1) A schema
for defining a tree structure that identifies and defines
certain objects that can be passed between units using
an SNMP protocol. The objects passed typically contain
certain information about the product such as the
physical or logical characteristics of the product. (2)
Shorthand for referring to the MIB-based record of a
network device. Information about a managed device is
defined and stored in the management information base
(MIB) of the device. Each ESS has a MIB. SNMP-based
network management software uses the record to
identify the device. See simple network management
protocol.
MAP. See maintenance analysis procedure.
Master Console. See IBM TotalStorage ESS Master
Console.
MB. See megabyte.
MCA. See Micro Channel architecture.
mean time between failures (MTBF). (1) A projection
of the time that an individual unit remains functional.
The time is based on averaging the performance, or
projected performance, of a population of statistically
independent units. The units operate under a set of
conditions or assumptions. (2) For a stated period in the
life of a functional unit, the mean value of the lengths of
time between consecutive failures under stated
conditions. (I) (A)
medium. For a storage facility, the disk surface on
which data is stored.
megabyte (MB). (1) For processor storage, real and
virtual storage, and channel volume, 2
20
or 1 048 576
bytes. (2) For disk storage capacity and
communications volume, 1 000 000 bytes.
MES. See miscellaneous equipment specification.
MIB. See management information base.
Micro Channel architecture (MCA). The rules that
define how subsystems and adapters use the Micro
Channel bus in a computer. The architecture defines the
services that each subsystem can or must provide.
Glossary 195
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