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channel path. The ESA/390 term for the
interconnection between a channel and its associated
control units.
channel subsystem. The ESA/390 term for the part of
a host computer that manages I/O communication
between the program and any attached control units.
channel-subsystem image. The ESA/390 term for the
logical facilities required to perform the function of a
channel subsystem. With EMIF, one channel-subsystem
image exists in the channel subsystem for each LPAR.
Each image appears to be an independent channel
subsystem program, but all images share a common set
of hardware facilities.
CKD. Count Key Data. An ESA/390 architecture for a
DASD 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 which can
contain one or more records, each consisting of a count
field, a key field (optional), and a data field (optional).
cluster. A partition of a storage controller that is
capable of performing all functions of a storage server.
Multiple clusters provide redundancy.
concurrent copy. A facility of a storage controller
used to assist a program in making a consistent copy of
a logical volume while the logical volume remains
available for subsequent processing.
concurrent maintenance. The ability to service a unit
while it is operating.
concurrent media maintenance. The ability to
perform maintenance on a disk drive module (DDM)
without loosing access to the data.
configure. To define the logical and physical
configuration of the input/output (I/O) subsystem via the
user interface provided for this function on the storage
facility.
consistent copy. A copy of a data entity (e.g. a logical
volume) that contains the contents of the entire data
entity from a single instant in time.
contingent allegiance. The ESA/390 term for a
relationship that is created in a control unit between a
device and a channel path when unit-check status is
accepted by the channel. The allegiance causes the
control unit to guarantee access (i.e. busy status is not
presented) to the device to retrieve the sense data
associated with the unit-check status on the channel
path associated with the allegiance.
control unit. The ESA/390 term for a storage
controller with ESCON or OEMI interfaces.
control-unit image. The ESA/390 term for a logical
subsystem accessed via an ESCON I/O Interface. One
or more control-unit images exist in each control unit.
Each image appears to be an independent control unit,
but all images share a common set of hardware
facilities.
count field. The first field of a CKD record. The
eight-byte field contains a four-byte track address
(CCHH) that defines the cylinder and head associated
with the track, a one-byte record number (R) that
identifies the record on the track, a one-byte key length
that specifies the length of the record's key field (0
means no key field), and 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.
CPAR. Customer Problem Analysis and Repair.
CPI. Common Platform Interconnect.
CPSS. Common Platform Storage Subsystems. A
strategy and family of storage products based on
common hardware parts.
CRC. Cyclic Redundancy Check.
CSU. Customer Set Up.
Customer Console. A user interface to a server. Also
see Versatile Storage Specialist.
Cyclic Redundancy Check (CRC). A data
redundancy check in which a cyclic algorithm generates
the check key.
cylinder. A unit of storage on a CKD device consisting
of a fixed number of tracks.
D
DA. Device Adapter, the SSA device card.
daisy chain. A method of device interconnection for
determining interrupt priority by connecting the interrupt
sources serially.
DASD. Direct Access Storage Device.
DASD fast write. A facility of a storage controller that
allows caching of active write data without exposure of
data loss by journaling of the active write data in NVS.
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 the data transfer
rates are balanced among the hosts.
data compression. A technique or algorithm used to
encode a quantity of data such that the encoded result
can generally be stored in less space than the original
data and such that the original data can be recovered
from the encoded result through a reverse technique or
reverse algorithm.
Glossary of Terms and Abbreviations
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