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configure. To define the logical and physical
configuration of the input/output (I/O) subsystem through
the user interface provided for this function on the
storage facility.
consistent copy. A copy of a data entity (for example
a logical volume) that contains the contents of the entire
data entity at a single instant in time.
console. A user interface to a server, such as a
personal computer.
contingent allegiance. In the ESA/390 architecture, a
relationship that is created in a controller between a
device and a channel path when unit-check status is
accepted by the channel. The allegiance causes the
controller to guarantee access; the controller does not
present the busy status to the device. This enables the
controller to retrieve sense data that is associated with
the unit-check status on the channel path with which the
allegiance is associated.
controller. In the ESA/390 architecture, a storage
controller with ESCON or OEMI interfaces. See cluster .
controller image. In the ESA/390 architecture, a
logical subsystem that you access with an ESCON I/O
interface. One or more control-unit images exist in each
controller. Each image appears to be an independent
controller, but all images share a common set of
hardware facilities.
control unit (CU). In System/390 architecture, a
storage control unit with ESCON or OEMI interfaces.
Also referred to as a controller.
Copy Services server group. A collection of ESS
clusters that participate in Copy Services functions that
include the volumes within the clusters.
count field. The first field of a 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 the ESA/390 architecture, a
logical device that specifies the format of and access
mechanisms for the logical data units on the device.
The logical data unit is a track that can contain one or
more records, each consisting of a count field, a key
field (optional), and a data field (optional).
CPC. See cluster processor complex .
CRC. See cyclic redundancy check .
CU. See control unit .
customer console. See console .
CUT. See Universaile Tempes du Coordinaire .
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. A cylinder
has a fixed number of tracks.
D
DA. See device adapter and SSA adapter .
daisy chain. A method of device interconnection for
determining interrupt priority by connecting the interrupt
sources serially.
DASD. See direct access storage device and disk
drive module .
DASD-fast write. A function of a storage controller
that allows caching of active write data without exposure
of data loss by journaling of the active write data in
nonvolatile storage.
data availability. The degree to which data is
available when needed. For better data availability when
you attach multiple hosts that share the same data
storage, configure the data paths so that data transfer
rates are balanced among the hosts.
data compression. A technique or algorithm that you
use to encode data such that you can store the
encoded result in less space than the original data. This
algorithm allows you to recover the original data from
the encoded result through a reverse technique or
reverse algorithm. See compression .
Data Facility Storage Management Subsystem. An
operating environment that helps automate and
centralize the management of storage. To manage
storage, SMS provides the storage administrator with
control over data class, storage class, management
class, storage group, and automatic class selection
routine definitions.
data field. The third (optional) field of a CKD record.
You determine the field length by the data length that is
specified in the count field. The data field contains data
that the program writes.
data record. A subsystem stores data records on a
track by following the track-description record. The
subsystem numbers the data records consecutively,
starting with 1. A track can store a maximum of 255
data records. Each data record consists of a count field,
a key field (optional), and a data field (optional).
data sharing. The ability of homogenous or divergent
host systems to concurrently utilize information that they
store on one or more storage devices. The storage
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Glossary
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