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96257 Sun Confidential: Internal Only C-95
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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.