Sun Microsystems StorageTek 96257 - Manual (Page 95)

96257 Sun Confidential: Internal Only C-95
Revision A
P
packet. A unit of data formatted for transmission on a
network. Each packet has a header containing its source
and destination, a block of data content, and an error-
checking code. The data packets for a specific message
may take different routes to a destination, and the pack-
ets are reassembled on arrival.
PAD. Packet assembly/disassembly. See packet.
PAL. Programmable Array Logic.
parallel. Side by side. A parallel interface transmits eight
bits (one byte) of data at a time, over eight parallel lines,
while a serial interface transmits only one bit at a time. A
parallel cable can use eight channels to transmit one
eight-bit byte at a time, or may transmit more than one
byte at a time. Some of the eight channels may be used
to transmit control signals instead of data. Contrast with
serial.
parity bit. A binary check digit inserted in an array of bi-
nary digits to make the arithmetic sum of all digits, in-
cluding the check digit, always odd or even (as was pre-
determined).
parity checking. A method of verifying the integrity of
data when it is transferred between entities (within a sub-
system, between a subsystem and host, etc.).
parity generation. Application of a mathematical algo-
rithm to ensure integrity of data transfers. Parity data is
generated and sent along with the original data to be in-
terpreted at the receiving end, validating the integrity of
the data.
partition. Logical separation of devices, arrays, or
groups of arrays within a VTSS to allow different func-
tionality (media acceptance test, production, spares, and
unavailable).
path. See storage path.
PCAP. Physical Capacity Control.
PCI. Peripheral Component Interconnect.
PCM. Power control module; plug-compatible manufac-
turer.
PDU. Power distribution unit.
physical. In VTSS, a view or description of actual hard-
ware or fixed locations, as opposed to conceptual or dy-
namic subsystem elements (functional tracks, logical
paths, virtual volumes). Contrast with functional, logical.
P/N. Part number.
preventive maintenance (PM). Routine, scheduled ac-
tion to prevent a machine from failing due to normal wear
and tear.
privileged ECAM device. A device type used by ExPR
to send messages to a VTSS to request a change in the
subsystem state. At least one privileged ECAM device
must be defined per subsystem; however, all functional
volumes can be defined as privileged ECAM devices.
production partition. In VSM, a partition state of VTSS
array drives used for storage of user data. Contrast with
media acceptance test partition, spares partition, un-
available partition.
PSA. Predictive Service Analysis. A VTSS Failure Man-
agement System function that receives failure reports
from the support facility, performs problem analysis, and
issues a suspect FRU list.
Program Configuration Document (PCD). A Sun
StorageTek document that provides a description of ar-
chitectural elements that comprise the internal structure
of a product. A PCD includes, among other things, a list-
ing of all available product configurations, including fea-
ture codes and part numbers used for ordering.
protocol. In command sequencing, the required com-
mands in the proper order and timing to invoke a desired
response. In data communication packets, a defined se-
quence of data patterns that follow a defined set of rules
for data exchange and error correction.
PSSIB. Power system serial interface bus.
PTF. Program Temporary Fix. An interim patch, or ‘fix’,
applied to a known defect in software or microcode.
Q
query. A request for data from a file or database, based
on specified conditions.
queue. (1) A line or list of commands waiting to be pro-
cessed. (2) A list constructed and maintained so that the
next data element to be retrieved is the one stored first.
quiesce. To end a process by allowing operations to
complete normally.
R
rack. A free-standing framework that holds equipment.
VSM4-VTSS uses an industry-standard 19-inch rack for
mounting the array drives and related components.
random access. A method of storing and retrieving in-
formation randomly, as on magnetic disk media. Any file
or piece of information stored in a random-access format
can be selected and accessed immediately in any order.
Contrast with serial access.
RAID. Redundant Arrays of Independent Disks.
RCSE. See remote customer service engineer.
read. To acquire or interpret data from a storage device,
a data medium, or another source.
read hit. An instance wherein data requested by a read
operation is found in cache.
read miss. An instance wherein data requested by a
read operation is not found in cache.
real tape drive (RTD). Physical transports (TimberLine
9490, RedWood SD-3, T9840x, T9940x) controlled by
VSM. The transport has a data path to a VTSS and may
optionally have a data path to MVS or to another VTSS.
recall. Movement of VTVs back to a VTSS from a MVC.
VSM provides ability to recall VTVs on demand.
reclaim. A space-reclamation function performed by a
MVC. VTCS uses the amount of fragmented free space
on a MVC and the amount of VTV data that would have
to be moved to determine if space reclamation is justi-
fied. VSM provides ability to reclaim MVCs on demand.
reconstruction. See device reconstruction.
redundancy group. A logical grouping of devices that
are protected against data loss from device failures by
the use of redundancy information that is stored across
the entire group of devices. VTSS dual-redundancy ar-
rays are redundancy groups that provide data protection
against two simultaneous device failures.