IBM DS8000 Channel command retry CCR, Channel command word CCW, Channel path, Channel subsystem

channel command retry (CCR)

For zSeries, the protocol used between a channel and a control unit that enables the control unit to request that the channel reissue the current command.

channel command word (CCW)

For zSeries, a data structure that specifies an I/O operation to the channel subsystem.

channel path

For zSeries, the interconnection between a channel and its associated control units.

channel subsystem

For zSeries, the part of a host computer that manages I/O communication between the program and any attached control units.

channel-subsystem image

For zSeries, 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. See also Copy Services command-line interface.

cluster

1)A partition capable of performing all DS8000 functions. With two clusters in the DS8000, any operational cluster can take over the processing of a failing cluster.

2)In the AIX operating system, a group of nodes within a complex.

cluster processor complex (CPC)

The unit within a cluster that provides the management function for the DS8000. It consists of cluster processors, cluster memory, and related logic.

command-line interface (CLI)

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 or

UNIX shell commands). See also Copy Services command-line interface.

compact disc

An optically read disc, typically storing approximately 660 MB. CD-ROM (compact disc read-only memory) refers to the read-only format used to distribute DS8000 code and documentation.

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. (GC)

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 a DS8000 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

In storage, to define the logical and physical configuration of the input/output (I/O) subsystem through the user interface that the storage unit provides for this function.

consistency group

A group of volumes participating in FlashCopy relationships in a logical subsystem, across logical subsystems, or across multiple storage units that must be kept in a consistent state to ensure data integrity.

328IBM TotalStorage DS8000: Messages Reference