Specifications

channel subsystem. In Enterprise Systems
Architecture/390, the part of a host computer that
manages I/O communication between the program and
any attached control units.
channel-subsystem image. In Enterprise Systems
Architecture/390, the logical functions that a system
requires to perform the function of a channel
subsystem. With ESCON multiple image facility (EMIF),
one channel subsystem image exists in the channel
subsystem for each logical partition (LPAR). Each image
appears to be an independent channel subsystem
program, but all images share a common set of
hardware facilities.
CKD. See count key data.
CLI. See command-line interface.
cluster. (1) A partition in the ESS capable of
performing all ESS functions. With two clusters in the
ESS, any operational cluster can take over the
processing of a failing cluster. (2) On an AIX platform, a
group of nodes within a complex.
cluster processor complex (CPC). The unit within a
cluster that provides the management function for the
storage server. It consists of cluster processors, cluster
memory, and related logic.
command-line interface (CLI). (1) An interface
provided by an operating system that defines a set of
commands and enables a user (or a script-like
language) to issue these commands by typing text in
response to the command prompt (for example, DOS
commands, UNIX shell commands). (2) An optional ESS
software that enables a user to issue commands to and
retrieve information from the Copy Services server.
compact disc, read-only memory (CD-ROM).
High-capacity read-only memory in the form of an
optically read compact disc.
compression. (1) The process of eliminating gaps,
empty fields, redundancies, and unnecessary data to
shorten the length of records or blocks. (2) Any
encoding that reduces the number of bits used to
represent a given message or record.
computer-electronic complex (CEC). The set of
hardware facilities associated with a host computer.
Concurrent Copy. A facility on a storage server that
enables a program to make a backup of a data set
while the logical volume remains available for
subsequent processing. The data in the backup copy is
frozen at the point in time that the server responds to
the request.
concurrent installation of licensed internal code.
Process of installing licensed internal code on an ESS
while applications continue to run.
concurrent maintenance. Service that is performed
on a unit while it is operational.
concurrent media maintenance. Service performed
on a disk drive module (DDM) without losing access to
the data.
configure. To define the logical and physical
configuration of the input/output (I/O) subsystem through
the user interface provided for this function on the
storage facility.
consistent copy. A copy of a data entity (a logical
volume, for example) that contains the contents of the
entire data entity at a single instant in time.
console. A user interface to a server, such as can be
provided by a personal computer. See IBM TotalStorage
ESS Master Console.
contingent allegiance. In Enterprise Systems
Architecture/390, a relationship that is created in a
control unit between a device and a channel when
unit-check status is accepted by the channel. The
allegiance causes the control unit to guarantee access;
the control unit does not present the busy status to the
device. This enables the channel to retrieve sense data
that is associated with the unit-check status on the
channel path associated with the allegiance.
control unit (CU). (1) A device that coordinates and
controls the operation of one or more input/output
devices, and synchronizes the operation of such
devices with the operation of the system as a whole. (2)
In Enterprise Systems Architecture/390, a storage
server with ESCON, FICON, or OEMI interfaces. The
control unit adapts a native device interface to an I/O
interface supported by an ESA/390 host system. On an
ESS, the control unit would be the parts of the storage
server that support the attachment of emulated CKD
devices over ESCON, FICON, or OEMI interfaces. See
cluster.
control-unit image. In Enterprise Systems
Architecture/390, a logical subsystem that is accessed
through an ESCON or FICON I/O interface. One or
more control-unit images exist in each control unit. Each
image appears as an independent control unit, but all
control-unit image share a common set of hardware
facilities. The ESS can emulate 3990-3, TPF, 3990-6, or
2105 control units.
control-unit initiated reconfiguration (CUIR). A
software mechanism used by the ESS to request that
an operating system verify that one or more subsystem
resources can be taken off-line for service. The ESS
can use this process to automatically vary channel
paths offline and online to facilitate bay service or
concurrent code installation. Depending on the
operating system, support for this process may be
model-dependent, may depend on the IBM Subsystem
Device Driver, or may not exist.
Glossary 187
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