IBM DS8000 - ADDITIONAL INFORMATION, Руководство пользователя, Страница: 218 / 250

Coordinated Universal Time (UTC)
The international standard of time that is
kept by atomic clocks around the world.
Copy Services
A collection of optional software features,
with a Web-browser interface, that is used
for configuring, managing, and
monitoring data-copy functions.
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)
In mainframe computing, 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 System z 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.
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.
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DS8000 User’s Guide