Specifications
common symbols. Some organizations, including IBM,
have used the parity bit to expand the basic code set.
assigned storage. On an ESS, the space allocated to
a volume and assigned to a port.
authorized program analysis report (APAR). A
report of a problem caused by a suspected defect in a
current, unaltered release of a program.
availability. The degree to which a system or resource
is capable of performing its normal function. See data
availability.
B
backup Copy Services server. One of two Copy
Services servers in a Copy Services domain. The other
Copy Services server is the primary Copy Services
server. The backup Copy Services server is available to
become the active Copy Services server if the primary
Copy Services server fails. A Copy Services server is
software that runs in one of the two clusters of an ESS,
and manages data-copy operations for that Copy
Services server group. See primary Copy Services
server and active Copy Services server.
bay. Physical space on an ESS used for installing
SCSI, ESCON, and fibre-channel host adapter cards.
The ESS has four bays, two in each cluster. See
service boundary.
bit. (1) A binary digit. (2) The storage medium required
to store a single binary digit. (3) Either of the digits 0 or
1 when used in the binary numeration system. (T) See
byte.
block. A group of consecutive bytes used as the basic
storage unit in fixed-block architecture (FBA). All blocks
on the storage device are the same size (fixed size).
See fixed-block architecture and data record.
byte. (1) A group of eight adjacent binary digits that
represent one EBCDIC character. (2) The storage
medium required to store eight bits. See bit.
C
cache. A buffer storage that contains frequently
accessed instructions and data, thereby reducing
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 hit. An event that occurs when a read operation
is sent to the cluster, and the requested data is found in
cache. The opposite of cache miss.
cache memory. Memory, typically 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. In addition to residing in cache memory, the
same data also resides on the storage devices in the
storage facility.
cache miss. An event that occurs when a read
operation is sent to the cluster, but the data is not found
in cache. The opposite of cache hit.
call home. A communication link established between
the ESS and a service provider. The ESS can use this
link to place a call to IBM or to another service provider
when it requires service. With access to the machine,
service personnel can perform service tasks, such as
viewing error logs and problem logs or initiating trace
and dump retrievals. See heartbeat and remote
technical assistance information network.
cascading. (1) Connecting network controllers to each
other in a succession of levels, to concentrate many
more lines than a single level permits. (2) In
high-availability cluster multiprocessing (HACMP),
cascading pertains 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.
The cluster node relinquishes the resource to the
primary node upon reintegration of the primary node
into the cluster.
catcher. A server that service personnel use to collect
and retain status data that an ESS sends to it.
CCR. See channel-command retry.
CCW. See channel command word.
CD-ROM. See compact disc, read-only memory.
CEC. See computer-electronic complex.
channel. In Enterprise Systems Architecture/390, the
part of a channel subsystem that manages a single I/O
interface between a channel subsystem and a set of
control units.
channel command retry (CCR). In Enterprise
Systems Architecture/390, the protocol used between a
channel and a control unit that enables the control unit
to request that the channel reissue the current
command.
channel command word (CCW). In Enterprise
Systems Architecture/390, a data structure that specifies
an I/O operation to the channel subsystem.
channel path. In Enterprise Systems Architecture/390,
the interconnection between a channel and its
associated control units.
186 ESS Host Systems Attachment Guide
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