Specifications

parallel access volume (PAV). An advanced function
of the ESS that enables OS/390 and z/OS systems to
issue concurrent I/O requests against a CKD logical
volume by associating multiple devices of a single
control-unit image with a single logical device. Up to 8
device addresses can be assigned to a parallel access
volume. PAV enables two or more concurrent writes to
the same logical volume, as long as the writes are not
to the same extents. See extent, I/O Priority Queueing,
and multiple allegiance.
parity. A data checking scheme used in a computer
system to ensure the integrity of the data. The RAID
implementation uses parity to recreate data if a disk
drive fails.
path group. The ESA/390 term for a set of channel
paths that are defined to a control unit as being
associated with a single logical partition (LPAR). The
channel paths are in a group state and are online to the
host. See logical partition.
path group identifier. The ESA/390 term for the
identifier that uniquely identifies a given logical partition
(LPAR). The path group identifier is used in
communication between the LPAR program and a
device. The identifier associates the path group with
one or more channel paths, thereby defining these
paths to the control unit as being associated with the
same LPAR.
PAV. See parallel access volume.
PCI. See peripheral component interconnect.
PE. See IBM product engineering.
Peer-to-Peer Remote Copy (PPRC). A function of a
storage server that maintains a consistent copy of a
logical volume on the same storage server or on
another storage server. All modifications that any
attached host performs on the primary logical volume
are also performed on the secondary logical volume.
peripheral component interconnect (PCI). An
architecture for a system bus and associated protocols
that supports attachments of adapter cards to a system
backplane.
physical path. A single path through the I/O
interconnection fabric that attaches two units. For Copy
Services, this is the path from a host adapter on one
ESS (through cabling and switches) to a host adapter
on another ESS.
point-to-point connection. For fibre-channel
connections, a topology that enables the direct
interconnection of ports. See arbitrated loop and
switched fabric.
POST. See power-on self test.
power-on self test (POST). A diagnostic test run by
servers or computers when they are turned on.
PPRC. See Peer-to-Peer Remote Copy.
predictable write. A write operation that can cache
without knowledge of the existing format on the
medium. All writes on FBA DASD devices are
predictable. On CKD DASD devices, a write is
predictable if it does a format write for the first data
record on the track.
primary Copy Services server. One of two Copy
Services servers in a Copy Services domain. The
primary Copy Services server is the active Copy
Services server until it fails; it is then replaced by the
backup Copy Services server. A Copy Services server is
software that runs in one of the two clusters of an ESS
and performs data-copy operations within that group.
See active Copy Services server and backup Copy
Services server.
product engineering. See IBM product engineering.
program. On a computer, a generic term for software
that controls the operation of the computer. Typically,
the program is a logical assemblage of software
modules that perform multiple related tasks.
program-controlled interruption. An interruption that
occurs when an I/O channel fetches a channel
command word with the program-controlled interruption
flag on.
program temporary fix (PTF). A temporary solution or
bypass of a problem diagnosed by IBM in a current
unaltered release of a program
promote. To add a logical data unit to cache memory.
protected volume. An AS/400 term for a disk storage
device that is protected from data loss by RAID
techniques. An AS/400 host does not mirror a volume
configured as a protected volume, while it does mirror
all volumes configured as unprotected volumes. The
ESS, however, can be configured to indicate that an
AS/400 volume is protected or unprotected and give it
RAID protection in either case.
pSeries. An IBM Eserver product that emphasizes
performance.
pseudo-host. A host connection that is not explicitly
defined to the ESS and that has access to at least one
volume that is configured on the ESS. The FiconNet
pseudo-host icon represents the FICON protocol. The
EsconNet pseudo-host icon represents the ESCON
protocol. The pseudo-host icon labelled “Anonymous”
represents hosts connected through the SCSI-FCP
protocol. Anonymous host is a commonly used synonym
for pseudo-host. The ESS adds a pseudo-host icon only
when the ESS is set to access-any mode. See
access-any mode.
Glossary 197
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