IBM Enterprise Storage Server 2105 E10, Introduction And Planning Manual

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block. A group of consecutive bytes.
byte. A group of eight adjacent binary digits that
represent one EBCDIC character.
C
cache. A buffer storage that contains frequently
accessed instructions and data; it is used to reduce
access time.
cache fast write. A form of the fast-write operation in
which the subsystem writes the data directly to cache
where it is available for later destaging.
cache memory. Typically refers to volatile memory
that a subsystem uses to improve access times to
instructions or data. The cache memory is typically
smaller and faster than the primary memory or storage
medium. A storage subsystem uses the cache memory
to improve the performance of accesses to data that
ultimately resides on the storage devices in the storage
facility.
cascading. The connecting of network controllers to
each other in a succession of levels, to concentrate
many more lines than a single level permits. In
high-availability cluster multiprocessing (HACMP),
pertaining to a cluster configuration in which the cluster
node with the highest priority for a particular resource
acquires the resource if the primary node fails but
relinquishes the resource to the primary node upon
reintegration of the primary node into the cluster
CCR. See channel-command retries.
CCW. See channel command word.
CEC. See computer-electronic complex.
channel. In the ESA/390 architecture, the part of a
channel subsystem that manages a single I/O interface
between a channel subsystem and a set of controllers.
channel-command retries (CCR). In the ESA/390
architecture, the protocol used between a channel and
a controller that allows the controller to request that the
channel reissue the current command.
channel command word (CCW). In the ESA/390
architecture, a data structure that is used to specify an
I/O operation to the channel subsystem.
channel path. In the ESA/390 architecture, the
interconnection between a channel and its associated
controllers.
channel subsystem. In the ESA/390 architecture, the
part of a host computer that manages I/O
communication between the program and any attached
controllers.
channel-subsystem image. In the ESA/390
architecture, the logical functions that a system requires
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. See count key data.
CLI. See command-line interface.
cluster. (1) A partition in a storage server that is
capable of performing all function of a storage server.
When there are multiple clusters in a storage server,
any remaining clusters in the configuration can take
over the processing of any failing clusters. (2) On an
AIX platform, a cluster is a group of nodes within a
complex.
cluster processor complex (CPC). The unit within a
cluster that provides the management function for the
storage server. It consists of cluster processors, cluster
memory, and related logic.
command-line interface. The command-line interface
on the open-systems hosts that initiates and manages
PPRC and FlashCopy on the ESS.
compact disc, read-only memory. High-capacity
read-only memory in the form of an optically read
compact disc.
compression. (1) The process of eliminating gaps,
empty fields, redundancies, and unnecessary data to
shorten the length of records or blocks. (2) Any
encoding to reduce the number of bits used to represent
a given message or record.
computer-electronic complex (CEC). The set of
hardware facilities associated with a host computer.
concurrent copy. Concurrent Copy allows a program
such as DFDSS to make a backup of a data set while
maintaining continuous read and write access to the
data. The data is frozen at the point in time that the
commands were issued to the controller.
concurrent download of licensed internal code.
Capability to download and install licensed internal code
on an ESS while applications continue to run
concurrent maintenance. Service that is performed
on a unit while it is operational.
concurrent media maintenance. Service performed
on a disk drive module (DDM) without losing access to
the data.
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ESS Introduction and Planning
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