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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.
330 IBM TotalStorage DS8000: Messages Reference