bootstrap protocol (BOOTP). In Transmission Control
Protocol/Internet Protocol (TCP/IP) networking, an
alternative protocol by which a diskless machine can
obtain its Internet Protocol (IP) address and such
configuration information as IP addresses of various
servers from a BOOTP server.
bridge. A storage area network (SAN) device that
provides physical and transport conversion, such as
fibre channel to small computer system interface (SCSI)
bridge.
bridge group. A bridge and the collection of devices
connected to it.
broadcast. The simultaneous transmission of data to
more than one destination.
cathode ray tube (CRT). A display device in which
controlled electron beams are used to display
alphanumeric or graphical data on an
electroluminescent screen.
client. A computer system or process that requests a
service of another computer system or process that is
typically referred to as a server. Multiple clients can
share access to a common server.
command. A statement used to initiate an action or
start a service. A command consists of the command
name abbreviation, and its parameters and flags if
applicable. A command can be issued by typing it on a
command line or selecting it from a menu.
community string. The name of a community
contained in each Simple Network Management
Protocol (SNMP) message.
concurrent download. A method of downloading and
installing firmware that does not require the user to
stop I/O to the controllers during the process.
CRC. See cyclic redundancy check.
CRT. See cathode ray tube.
CRU. See customer replaceable unit.
customer replaceable unit (CRU). An assembly or
part that a customer can replace in its entirety when
any of its components fail. Contrast with field replaceable
unit (FRU).
cyclic redundancy check (CRC). (1) A redundancy
check in which the check key is generated by a cyclic
algorithm. (2) An error detection technique performed
at both the sending and receiving stations.
dac. See disk array controller.
dar. See disk array router.
DASD. See direct access storage device.
data striping. See striping.
default host group. A logical collection of discovered
host ports, defined host computers, and defined host
groups in the storage-partition topology that fulfill the
following requirements:
v Are not involved in specific logical drive-to-LUN
mappings
v Share access to logical drives with default logical
drive-to-LUN mappings
device type. Identifier used to place devices in the
physical map, such as the switch, hub, or storage.
DHCP. See Dynamic Host Configuration Protocol.
direct access storage device (DASD). A device in
which access time is effectively independent of the
location of the data. Information is entered and
retrieved without reference to previously accessed data.
(For example, a disk drive is a DASD, in contrast with
a tape drive, which stores data as a linear sequence.)
DASDs include both fixed and removable storage
devices.
direct memory access (DMA). The transfer of data
between memory and an input/output (I/O) device
without processor intervention.
disk array controller (dac). A disk array controller
device that represents the two controllers of an array.
See also disk array router.
disk array router (dar). A disk array router that
represents an entire array, including current and
deferred paths to all logical unit numbers (LUNs)
(hdisks on AIX). See also disk array controller.
DMA. See direct memory access.
domain. The most significant byte in the node port
(N_port) identifier for the fibre-channel (FC) device. It
is not used in the fibre channel-small computer system
interface (FC-SCSI) hardware path ID. It is required to
be the same for all SCSI targets logically connected to
an FC adapter.
drive channels. The DS4200, DS4700, DS4800, and
DS5000 subsystems use dual-port drive channels that,
from the physical point of view, are connected in the
same way as two drive loops. However, from the point
of view of the number of drives and enclosures, they
are treated as a single drive loop instead of two
different drive loops. A group of storage expansion
enclosures are connected to the DS4000/DS5000 storage
subsystems using a drive channel from each controller.
This pair of drive channels is referred to as a redundant
drive channel pair.
drive loops. A drive loop consists of one channel from
each controller combined to form one pair of redundant
drive channels or a redundant drive loop. Each drive
168 IBM System Storage DCS3700: Installation, User, and Maintenance Guide
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