IBM DS8000 manual Availability, Cache fast write, Cache hit, Cache memory, Cache miss, Call home

availability

The degree to which a system or resource is capable of performing its normal function. See data availability.

B

bay The physical space that is used for installing SCSI, ESCON, and fibre-channel host adapter cards. The DS8000 has four bays, two in each cluster. See also service boundary.

bit 1) Either of the digits 0 or 1 when used in

the binary numeration system. (T)

2)The storage medium required to store a single binary digit. See also byte.

block A string of data elements recorded or transmitted as a unit. The elements may be characters, words, or physical records.

(T)

A group of consecutive bytes used as the basic storage unit in fixed-block architecture (FBA). All blocks on the storage device are the same size (fixed size). See also fixed-block architecture and data record.

byte 1) A group of eight adjacent binary digits that represent one EBCDIC character.

2)The storage medium required to store eight bits. See also bit.

C

cache A special-purpose buffer storage, smaller and faster than main storage, used to hold a copy of instructions and data obtained from main storage and likely to be needed next by the processor. (T)

cache fast write

A form of the fast-write operation in which the storage server writes the data directly to cache, where it is available for later destaging.

cache hit

An event that occurs when a read operation is sent to the cluster, and the requested data is found in cache. Contrast with cache miss.

cache memory

Memory, typically volatile memory, that a storage server uses to improve access times to instructions or data. The cache

memory is typically smaller and faster than the primary memory or storage medium. In addition to residing in cache memory, the same data also resides on the storage devices in the storage unit.

cache miss

An event that occurs when a read operation is sent to the cluster, but the data is not found in cache. Contrast with cache hit.

call home

A communication link established between the DS8000 and a service provider. The DS8000 can use this link to place a call to IBM or to another service provider when it requires service. With access to the machine, service personnel can perform service tasks, such as viewing error logs and problem logs or initiating trace and dump retrievals. See also heartbeat and remote technical assistance information network.

cascading

1)Connecting network controllers to each other in a succession of levels to concentrate many more lines than a single level permits.

2)In high-availability cluster multiprocessing (HACMP), cascading pertains to a cluster configuration in which the cluster node with the highest priority for a particular resource acquires the resource if the primary node fails. The cluster node relinquishes the resource to the primary node upon reintegration of the primary node into the cluster.

catcher

A server that service personnel use to collect and retain status data that an DS8000 sends to it.

CCR See channel command retry.

CCW See channel command word.

CD See compact disc.

CEC See computer-electronic complex.

channel

For zSeries, the part of a channel subsystem that manages a single I/O interface between a channel subsystem and a set of control units.

Glossary 327