IBM System Storage Subsystem DS5020 - Manual (Page 239)

Standard Architecture (EISA) bus. ISA and EISA boards
plug into an IA or EISA slot, while high-speed PCI
controllers plug into a PCI slot. See also Industry
Standard Architecture, Extended Industry Standard
Architecture.
polling delay. The time in seconds between
successive discovery processes during which discovery
is inactive.
port. A part of the system unit or remote controller to
which cables for external devices (such as display
stations, terminals, printers, switches, or external
storage units) are attached. The port is an access point
for data entry or exit. A device can contain one or more
ports.
portable document format (PDF). A standard
specified by Adobe Systems, Incorporated, for the
electronic distribution of documents. PDF files are
compact; can be distributed globally by e-mail, the Web,
intranets, or CD-ROM; and can be viewed with the
Acrobat Reader, which is software from Adobe Systems
that can be downloaded at no cost from the Adobe
Systems home page.
premium feature key. A file that the storage
subsystem controller uses to enable an authorized
premium feature. The file contains the feature enable
identifier of the storage subsystem for which the
premium feature is authorized, and data about the
premium feature. See also feature enable identifier.
private loop. A freestanding arbitrated loop with no
fabric attachment. See also arbitrated loop.
program temporary fix (PTF). A temporary solution or
bypass of a problem diagnosed by IBM in a current
unaltered release of the program.
PTF. See program temporary fix.
RAID. See redundant array of independent disks
(RAID).
RAID level. An array RAID level is a number that
refers to the method used to achieve redundancy and
fault tolerance in the array. See also array, redundant
array of independent disks (RAID).
RAID set. See array.
RAM. See random-access memory.
random-access memory (RAM). A temporary storage
location in which the central processing unit (CPU)
stores and executes its processes. Contrast with DASD.
RDAC. See redundant disk array controller.
read-only memory (ROM). Memory in which stored
data cannot be changed by the user except under
special conditions.
recoverable virtual shared disk (RVSD). A virtual
shared disk on a server node configured to provide
continuous access to data and file systems in a cluster.
redundant array of independent disks (RAID). A
collection of disk drives (array) that appears as a single
volume to the server, which is fault tolerant through an
assigned method of data striping, mirroring, or parity
checking. Each array is assigned a RAID level, which is
a specific number that refers to the method used to
achieve redundancy and fault tolerance. See also array,
parity check, mirroring, RAID level, striping.
redundant disk array controller (RDAC). (1) In
hardware, a redundant set of controllers (either
active/passive or active/active). (2) In software, a layer
that manages the input/output (I/O) through the active
controller during normal operation and transparently
reroutes I/Os to the other controller in the redundant set
if a controller or I/O path fails.
remote mirroring. Online, real-time replication of data
between storage subsystems that are maintained on
separate media. The Enhanced Remote Mirror Option is
a DS5020 premium feature that provides support for
remote mirroring. See also Global Mirroring, Metro
Mirroring.
ROM. See read-only memory.
router. A computer that determines the path of
network traffic flow. The path selection is made from
several paths based on information obtained from
specific protocols, algorithms that attempt to identify the
shortest or best path, and other criteria such as metrics
or protocol-specific destination addresses.
RVSD. See recoverable virtual shared disk.
SAI. See Storage Array Identifier.
SA Identifier. See Storage Array Identifier.
SAN. See storage area network.
SATA. See serial ATA.
scope. Defines a group of controllers by their Internet
Protocol (IP) addresses. A scope must be created and
defined so that dynamic IP addresses can be assigned
to controllers on the network.
SCSI. See small computer system interface.
segmented loop port (SL_port). A port that allows
division of a fibre-channel private loop into multiple
segments. Each segment can pass frames around as
an independent loop and can connect through the fabric
to other segments of the same loop.
sense data. (1) Data sent with a negative response,
indicating the reason for the response. (2) Data
describing an I/O error. Sense data is presented to a
host system in response to a sense request command.
Glossary 209