EMC Symmetrix DMX-3 Product Guide
311
Glossary
commands that are accepted by a device that employs the CKD
recording format.
D
DASD Direct access storage device.
data availability Access to user data at all times by the application.
delayed fast write An operation used when there is no room in global memory for the
data presented by the write operation. Therefore, the write is delayed
until there is room in global memory.
destage The asynchronous write of new or updated data from global memory
to disk drive.
device A uniquely addressable part of the Symmetrix subsystem that
consists of a set of access arms, the associated disk surfaces, and the
electronic circuitry required to locate, read, and write data. See also
“volume.”
device address The hexadecimal value that uniquely defines a physical I/O device
on a channel path in an MVS environment. See also unit address.
device form factor Refers to the physical size and shape of a device. Example: 73 GB disk
drive is a 1-in disk drive in a 3.5-in form factor.
device number The value that logically identifies a disk drive in a string.
device support
facilities program
(ICKDSF)
A program used to initialize the Symmetrix system at installation and
provide media maintenance.
diagnostics System-level tests or firmware designed to inspect, detect, and correct
failing components. These tests are comprehensive and self-invoking.
director See “channel director” or “disk director”.
disk director The component in the Symmetrix subsystem that interfaces between
global memory and the disk drives.
dual-initiator A Symmetrix feature that automatically creates a backup data path to
the disk drives serviced directly by a disk director, if that disk director
or the disk management hardware for those devices fails.
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