IBM Enterprise Storage Server 2105 E10 Introduction And Planning Manual page 134

facility allows configured storage to be accessible to
any, or all, attached host systems. To use this capability,
you need to design the host program to support data
that it is sharing.
DDM. See disk drive module .
DDM group. See disk drive module group .
dedicated storage. Storage within a storage facility
that is configured such that a single host system has
exclusive access to the storage.
demote. The action of removing a logical data unit
from cache memory. A subsystem demotes a data unit
in order to make room for other logical data units in the
cache. It could also demote a data unit because the
logical data unit is not valid. A subsystem must destage
logical data units with active write units before they are
demoted.
destaging. The moving of data from an online or
higher priority device to an offline or low priority device.
device. In the ESA/390 architecture, a disk drive.
device adapter (DA). A physical subunit of a storage
controller that provides the ability to attach to one or
more interfaces used to communicate with the
associated storage devices.
device address. In the ESA/390 architecture, the field
of an ESCON device-level frame that selects a specific
device on a control-unit image.
device interface card. A physical subunit of a storage
cluster that provides the communication with the
attached DDMs.
device number. (1) In the ESA/390 architecture, a
four-hexadecimal-character identifier, for example 13A0,
that you associate with a device to facilitate
communication between the program and the host
operator. (2) The device number that you associate with
a subchannel.
device sparing. A subsystem function that
automatically copies data from a failing DDM to a spare
DDM. The subsystem maintains data access during the
process.
direct access storage device (DASD). A mass
storage medium on which a computer stores data.
disk drive module (DDM). The primary nonvolatile
storage medium that you use for any host data that is
stored within a subsystem. The number and type of
storage devices within a storage facility may vary.
disk drive module group. A group of eight disk drive
modules (DDMs). Each DDM group is a RAID array.
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ESS Introduction and Planning
domain. (1) That part of a computer network in which
the data processing resources are under common
control. (2) In TCP/IP, the naming system used in
hierarchical networks.
drawer. A unit that contains multiple DDMs and
provides power, cooling, and related interconnection
logic to make the DDMs accessible to attached host
systems.
drive. (1) A peripheral device, especially one that has
addressed storage media. (2) The mechanism used to
seek, read, and write information on a storage medium.
duplex. A communication mode in which data can be
sent and received at the same time.
dynamic sparing. The ability of a storage server to
move data from a failing disk drive module (DDM) to a
spare DDM while maintaining storage functions.
E
EBCDIC. See extended binary-coded decimal
interchange code .
EC. See engineering change .
ECKD. See extended count key data .
electrostatic discharge (ESD). An undesirable
discharge of static electricity that can damage
equipment and degrade electrical circuitry.
emergency power off (EPO). A means of turning off
power during an emergency, usually a switch.
EMIF. See ESCON multiple image facility .
enclosure. A unit that houses the components of a
storage subsystem, such as a controller, disk drives,
and power source.
end of file. A coded character recorded on a data
medium to indicate the end of the medium. On a CKD
direct access storage device, the subsystem indicates
the end of a file by including a record with a data length
of zero.
engineering change (EC). An update to a machine,
part, or program.
Enterprise Systems Architecture/390 (ESA/390). An
IBM architecture for mainframe computers and
peripherals. Processor systems that follow this
architecture include the ES/9000
Enterprise Systems Connection (ESCON). (1) An
ESA/390 computer peripheral interface. The I/O
interface uses ESA/390 logical protocols over a serial
interface that configures attached units to a
communication fabric. (2) A set of IBM products and
®
family.