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96257 Sun Confidential: Internal Only C-89
Revision A
digital. Information stored in binary form that a computer
recognizes. For computing use, text, graphics, and
sound are stored as digital bits represented by a 0 or 1.
Contrast with analog.
dimmed text. Dimmed or grayed-out text that appears
on a GUI menu and indicates an option is unavailable
because the system is not in the mode to use that func-
tion, or because software for that function is not installed.
Available options are typically displayed in undimmed
black text.
director. A logical entity that interfaces host channels to
a disk device. See also multipath storage director
.
disk array. See dual-redundancy disk array
.
disk array capacity. Formatted physical capacity of an
array, exclusive of capacity on redundancy/parity drives
or spare drives.
disk array controller. In VTSS, a control unit that imple-
ments storage management functions and provides in-
terface intelligence between hosts or network devices
and VTSS arrays.
disk drive. An electromagnetic mechanical device that
provides physical data storage on magnetic disk media.
DLF. See Download Facility
.
DLT. Digital Linear Tape.
DMA. Direct Memory Access.
DMGR. See Diagnostic Manager
.
DNS. Domain Name Server.
download. To receive files or data from one storage de-
vice or computer to another. Contrast with upload
.
Download Facility (DLF). A VTSS facility that formats
event log data and connects to a RRC PC to offload
event log and MIM information as directed by the VTSS
PSA facility and subsystem internal timers.
drain. A process that gradually moves data stored from
an individual drive, drive array, or entire array unit to al-
low for eventual nondisruptive deinstallation of the
drive(s) or unit.
drive reconstruction. See device reconstruction
.
driver. A software routine that controls or regulates a
hardware device.
DSP. Digital signal processor.
dual copy. A function of VTSS nonvolatile storage that
maintains two functionally identical copies of designated
disk volumes in a logical subsystem, and automatically
updates both copies each time a write operation is is-
sued to a logical volume.
dual-redundancy disk array. In VSM, a logical grouping
of physical disk storage devices on a VTSS. In an array
five disk drives are reserved for user data, and two are
used for redundancy/parity data. Dual-redundancy ar-
rays allow for real time automatic recovery of data on up
to two failed devices within an array.
duplex. Bidirectional; a two-fiber or two-element cable
that provides two-way data transmission, i.e., it can si-
multaneously send and receive data. Contrast with sim-
plex.
duplexing. In VSM, the process of writing a virtual tape
volume (VTV) on two discrete multi-volume cartridges
(MVCs).
Dynamic Configuration. A VTSS feature that allows
channel interfaces and up to 1024 functional volumes to
be defined and/or altered. Allows the functional configu-
ration of a VTSS to be determined by user requirements
rather than by available physical devices.
Dynamic Director. A VTSS feature that allows dynamic
switching of ESCON director links between the VTSS
and RTDs for optimum system performance.
dynamic mapping. A VTSS mapping technique that dy-
namically alters the correspondence between a function-
al track and its location on physical devices, thereby
avoiding ‘update-in-place’, a major performance bottle-
neck in conventional RAID architectures. See also map-
ping. Contrast with fixed mapping.
E
earth grounding. An electrical connection to the earth
that is used to drain electrostatic charge from personnel
and equipment.
EC. Engineering Change.
ECA. ESCON channel adapter.
ECAM. Extended Control and Monitoring. A VTSS com-
munications protocol that permits communication be-
tween ExPR and the VTSS.
ECAM device. A functional host device number over
which ExPR-based communication takes place between
a controller and host CPU(s).
ECAMT. Extended Control and Monitoring for Tape.
ECAMT device. A functional device over which VTCS
communication between the VTSS disk array controller
and the host CPU(s) takes place.
ECC. See error correction code
.
ECN. Engineering Change Notice.
EDAC. Error detection and correction. A system that de-
tects and corrects errors during data transfers.
EEPROM. Electronically Erasable Programmable Read-
Only Memory.
electromagnetic interference (EMI). Leakage of radia-
tion from a high-frequency energy transmission source
that can cause interference to equipment or radio servic-
es. National and international regulatory agencies set
limits for EMI emissions. Class A limits apply to equip-
ment for industrial use; Class B limits apply to equipment
for non-commercial residential use.
EPO. Emergency Power Off. A safety switch on a ma-
chine or in a data center that allows a user to immediate-
ly power down a machine or a data center power supply
by cutting off the external source power.
EMI. See electromagnetic interference
.
EMIF. ESCON Multiple Image Facility
enterprise. A large-scale, organization-wide computer
network that may include web-based, client-server, and
mainframe computing technologies.
Enterprise Systems Connection (ESCON). (1) A set of
fiber optic-based products and services developed by
IBM that allows devices within a storage environment to
be dynamically configured. (2) A channel-to-control unit
I/O interface that uses optical cables as a transmission
medium.