Copy Services server

A cluster that the Copy Services administrator designates to perform the DS8000 Copy Services functions.

Copy Services server group

A collection of user-designated DS8000 clusters participating in Copy Services functions that a designated, active, Copy Services server manages. A Copy Services server group is also called a Copy Services domain.

count field

The first field of a count key data (CKD) record. This eight-byte field contains a four-byte track address (CCHH). It defines the cylinder and head that are associated with the track, and a one-byte record number (R) that identifies the record on the track. It defines a one-byte key length that specifies the length of the record’s key field (0 means no key field). It defines a two-byte data length that specifies the length of the record’s data field (0 means no data field). Only the end-of-file record has a data length of zero.

count key data (CKD)

For zSeries, a data-record format employing self-defining record formats in which each record is represented by up to three fields: a count field that identifies the record and specifies its format, an optional key field that identifies the data area contents, and an optional data field that typically contains the user data. For CKD records on the storage unit, the logical volume size is defined in terms of the device emulation mode (3390 or 3380 track format). The count field is always 8 bytes long and contains the lengths of the key and data fields, the key field has a length of 0 to 255 bytes, and the data field has a length of 0 to 65 535 or the maximum that will fit on the track. See also data record.

CPC See cluster processor complex. CRC See cyclic redundancy check. CU See control unit.

CUIR See control-unit initiated reconfiguration.

custom volume

A volume in count-key-data (CKD) format that is not a standard volume, which means that it does not necessarily present

the same number of cylinders and capacity to its assigned logical control unit as provided by one of the following standard zSeries volume types: 3390-2, 3390-3, 3390-9, 3390-2 (3380-track mode), or 3390-3 (3380-track mode). See also count-key-data, interleave, standard volume, and volume.

CUT See Coordinated Universal Time.

cyclic redundancy check (CRC)

A redundancy check in which the check key is generated by a cyclic algorithm. (T)

cylinder

A unit of storage on a CKD device with a fixed number of tracks.

D

DA See device adapter. See also IBM Serial Storage adapter.

daisy chain

See serial connection.

DASD See direct access storage device.

DASD fast write (DFW)

A function of a storage server in which active write data is stored in nonvolatile cache, thus avoiding exposure to data loss.

data availability

The degree to which data is available when needed, typically measured as a percentage of time that the system would be capable of responding to any data request (for example, 99.999% available).

data compression

A technique or algorithm used to encode data such that the encoded result can be stored in less space than the original data. The original data can be recovered from the encoded result through a reverse technique or reverse algorithm. See also compression.

Data Facility Storage Management Subsystem (DFSMS)

An operating environment that helps automate and centralize the management of storage. To manage storage, DFSMS provides the storage administrator with control over data class, storage class, management class, storage group, and automatic class selection routine definitions.

330IBM TotalStorage DS8000: Messages Reference

Page 350
Image 350
IBM DS8000 Copy Services server group, Count field, Count key data CKD, Custom volume, Cyclic redundancy check CRC