[Services] Acronym for Platform as a Service.


[Computer System] A colloquial term describing a software program’s reaction to an incomprehensible state.

In an operating system context, a panic is usually a system call, triggered by an unexpected state, that causes the system to abruptly stop executing. This is intended to reduce the possibility that the cause of the panic will cause further damage to the system, applications, or data and hopefully to preserve the system in a viable enough state that it can store debugging information in a safe place for analysis once it has come back up.

parallel access array

[Storage System] A disk array model in which data transfer and data protection algorithms assume that all member disks operate in unison, with each participating in the execution of every application I/O request.

A parallel access array is only capable of executing one I/O request at a time. True parallel access would require that an array's disks be rotationally synchronized. In actual practice, arrays approximate parallel access behavior. Ideal RAID Level 2 and RAID Level 3 arrays are parallel access arrays. See Independent access array.

parallel (transmission)

[Network] Simultaneous transmission of multiple data bits over multiple physical lines.

parity data

[Storage System] In a RAID array, data stored on member disks that can be used for regenerating any user data that becomes inaccessible.

Parity data is usually calculated by taking the XOR of the data on the member disks.

parity disk

[Storage System] In a RAID Level 3 or 4 array and some Level 6 arrays, a dedicated disk on which parity check data is stored.

parity RAID

[Storage System] A collective term used to refer to Berkeley RAID Levels 3, 4, 5 and 6.

parity RAID array

[Storage System] A RAID array whose data protection mechanism is one of Berkeley RAID Levels 3, 4, 5 or 6.


1. [Storage System] A subdivision of the capacity of a physical or virtual disk.

2. [Storage System] A contiguously addressed range of logical blocks on a physical media that is identifiable by an operating system.

Partitions are consecutively numbered ranges of blocks that are created and used by MS-DOS, Windows, and most UNIX operating systems.


[Storage System] Presentation of the usable storage capacity of a disk or array to an operating environment in the form of several virtual disks whose aggregate capacity approximates that of the underlying physical or virtual disk.

Partitioning is common in MS-DOS, Windows, and UNIX environments. Partitioning is useful with hosts that cannot support the full capacity of a large disk or array as one device. It can also be useful administratively, for example, to create hard subdivisions of a large virtual disk.


[Data Security] A sequence of characters longer than the acceptable length of a password that is transformed by a password system into a virtual password of acceptable length.


[Data Security] A private alphanumeric string used to authenticate an identity.

password digest

[Data Security] The hashed form of a cleartext password.


1. [Storage System] The access path from a host computer to a storage device.

2. [File System] The combination of device address and file system directory elements used to locate a file within a file system.

3. [Network] Any route through an interconnect that allows two devices to communicate.

4. [Computer System] A sequence of computer instructions that performs a given function, such as I/O request execution.

5. [Cloud] The access path from an internet-connected computer to a cloud service endpoint, typically in the form of a URI or URL.

path length

1. [Computer System] The number of instructions (a rough measure of the amount of time) required by a computer to perform a specific activity, such as I/O request execution.

2. [Data Recovery] [File System] The number of characters in a path name.

path name

[File System] The complete list of nested sub-directories through which a file is reached.


[Fibre Channel] [Network] Contents of the data field of a communications frame or packet.

In Fibre Channel, the payload excludes optional headers and fill bytes, if they are present.


[Computer System] Shorthand for Petabyte (1015 bytes).


[General] Shorthand for Petabit.


[Fibre Channel] Acronym for Port Bypass Circuit.


[Computer System] Acronym for Peripheral Component Interconnect.

PCI Express Queuing Interface (PQI)

[SCSI] A circular queue interface for transferring information between a host and a device on a PCI Express bus or fabric.


[File System] A daemon that permits personal computers to access file systems via the NFS protocol.


1. [Network] [iSCSI] Acronym for Protocol Data Unit.

2. [Computer System] Acronym for Power Distribution Unit.

Pebibit (Pibit)

[General] Shorthand for 1,125,899,906,842,624 (250) bits.

Binary notation is most commonly used for semiconductor memory sizes.

See also Petabit.

Pebibyte (PiB)

[General] Shorthand for 1,125,899,906,842,624 (250) bytes.

Binary notation is most commonly used for semiconductor memory sizes.

See also Petabyte.


[Computer System] One of two complimentary but physically separate systems.

For example, when user data is copied from a local system to a remote system, the remote system is considered the “peer” of the local system, and vice versa.


[Data Security] An unauthorized bypassing of the security mechanisms of a system.

penetration testing

[Data Security] A test methodology that attempts to circumvent or defeat the security features of an information system.

performance audit

[Computer System] Systematic evaluation of a system by assessing how well it conforms to a set of established performance criteria.

Peripheral Component Interconnect (PCI)

[Computer System] A bus for connecting interface modules to a computer system.

Older variations of PCI support 32 and 64 bit parallel data transfers at 33 and 66 MHz cycle times. The newer PCIe interface supports one bit wide serial "lanes" operating at 250MB/sec or 500MB/sec.

permanent deletion

[Data Management] The process of reliably and provably eliminating the ability, to a given level of assurance, to discover, recover, and read from digital media.

This process has two phases. The first phase is identifying all of the instances (including the physical locations) of the data to be deleted regardless of where it is located; the second phase is permanently destroying all traces of the data. Depending on the level of assurance required, complete physical destruction of the media may be necessary. See data shredding.

Legal considerations may also require maintenance of an audit trail of the above steps.

Permanent Port Name

[Fibre Channel] The Name_Identifier common among all N_Ports that are associated with the same physical interface, and is set to the F_Port_Name of the F_Port that is attached to the physical interface.


[Computer System] A synonym for non-volatility, usually used to distinguish between data and metadata held in DRAM, which is lost when electrical power is lost, and data held on non-volatile storage (disk, tape, battery-backed DRAM, etc.) that survives, or persists across power outages.

persistent memory access model

[Computer System] Semantic definition of how software accesses persistent memory hardware

persistent memory hardware

[Computer System] NVRAM that is byte addressable.

Personally Identifiable Information (PII)

[Data Security] Information associated with a person, as defined in ISO/IEC 29100.

Petabit (Pbit)

[General] Shorthand for 1,000,000,000,000,000 (1015) bits.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,125,899,906,842,624, i.e., 250) common in computer system and software literature.

See also Pebibit.

Petabyte (PB)

[Computer System] Shorthand for 1,000,000,000,000,000 (1015) bytes.

The SNIA uses the base 10 convention commonly found in I/O-related and scientific literature rather than the base 2 convention (1,125,899,906,842,624, i.e., 250) common in computer system and software literature.

See also Pebibyte.


[SCSI] A transceiver used to set up physical links between SCSI  devices.

There are different transceivers for each transport protocol. SAS, for example, uses four wires that comprise two differential signal pairs. Some other fabrics use an optical cable.

physical block

[Storage System] A physical area on a recording media at which data is stored, as distinguished from the logical and virtual block views typically presented to the operating environment by storage devices.

physical block address

[Storage System] The address of a physical block, i.e., a number that can be algorithmically converted to a physical location on storage media.

physical configuration

[General] The installation, removal, or re-installation of disks, cables, HBAs, and other components required for a system or subsystem to function.

Physical configuration is typically understood to include address assignments, such as PCI slot number, SCSI target ID and Logical Unit Number, etc. See array configuration, configuration.

physical disk

1. [Storage System] A disk that is not virtual.

2. [Operating System] A host operating system's view of an online storage device.

physical extent

[Storage System] A number of consecutively addressed blocks on a physical disk.

Physical extents are created by control software as building blocks from which redundancy groups and volume sets are created. Called a p_extent by ANSI.

physical extent block number

[Storage System] The relative position of a block within a physical extent.

Physical extent block numbers are used to develop higher-level constructs in RAID array striped data mapping, not for application or data addressing.


[General] Shorthand for Pebibit.


[General] Shorthand for Pebibyte.


[Data Security] Acronym for Personally Identifiable Information.


[Data Security] Acronym for Public Key Cryptography Standards.


[Data Security] Acronym for Public Key Infrastructure.


[Data Security] Unencrypted information.


[Fibre Channel] A physical entity that contains nodes.

Platforms include all end devices that are attached to a Fabric, for example, hosts and storage subsystems. Platforms communicate with other platforms in the storage area network using the facilities of a Fabric or other topology

Platform as a Service (PaaS)

[Services] Delivery over a network of a virtualized programming environment, consisting of an application deployment stack based on a virtual computing environment.

Typically, PaaS is based on IaaS, is either self-provisioned or provisionless, and is billed based on consumption.


[Fibre Channel] Acronym for Private Loop Direct Attach.


[Fibre Channel] Shorthand for Port Login.


[Fibre Channel] A Fibre Channel Link Control Facility (that is, a Fibre Channel physical port) in a node

point of encryption

[Data Security] Location within the Information and Communications Technology (ICT) infrastructure where data are encrypted on its way to storage (3.43) and, conversely, where data are decrypted when accessed from storage.
[ISO/IEC 27040]

The point of encryption is only applicable for data at rest.

Point In Time copy (PIT copy)

[Data Recovery] A fully usable copy of a defined collection of data that contains an image of the data as it appeared at a single instant in time.

A PIT copy is considered to have logically occurred at that point in time, but implementations may perform part or all of the copy at other times (e.g., via database log replay or rollback) as long as the result is a consistent copy of the data as it appeared at that point in time. Implementations may restrict point in time copies to be read-only or may permit subsequent writes to the copy. Three important classes of point in time copies are split mirror, changed block, and concurrent. Pointer remapping and copy on write are implementation techniques often used for the latter two classes. See snapshot.

pointer copy

[Data Recovery] A point in time copy made using the pointer remapping technique.

pointer remapping

[Data Recovery] A technique for maintaining a point in time copy in which pointers to all of the source data and copy data are maintained.

When data is overwritten, a new location is chosen for the updated data, and the pointer for that data is remapped to point to it. If the copy is read-only, pointers to its data are never modified. See Copy on Write.

policy (from RFC 3198)

1. [General] A definite goal, course or method of action to guide and determine present and future decisions.

2. [Management] Policies as a set of rules to administer, manage, and control access to network resources [RFC 3060].

Policies are implemented or executed within a particular context, such as policies defined within a business unit. See policy goal and policy rule.

policy goal (from RFC 3198)

[Management] Goals are the objectives or desired state intended to be maintained by a policy system.

As the highest level of abstraction of policy, these goals are most directly described in business rather than technical terms. For example, a goal might state that a particular application operate on a network as though it had its own dedicated network, despite using a shared infrastructure. 'Policy goals' can include the objectives of a service level agreement, as well as the assignment of resources to applications or individuals. A policy system may be created that automatically strives to achieve a goal through feedback regarding whether the goal (such as a service level) is being met.

policy processor

[Computer System] In an intelligent device, the processor that schedules the overall activities.

Policy processors are usually augmented by additional processors, state machines, or sequencers that perform the lower-level functions required to implement overall policy.

policy rule (from RFC 3198)

[Management] A basic building block of a policy-based system; the binding of a set of actions to a set of conditions, where the conditions are evaluated to determine whether the actions are performed [RFC 3060].


1. [Network] An entrance to or exit from a storage network.

2. [Network] A connection point for a peripheral device or an application program.

Ports can be logical, physical or both. Examples include Fibre Channel Ports, Internet Protocol Suite Ports and SCSI Ports.


[Fibre Channel] Formally referenced as N_Port_ID, a unique 24 bit address used for frame routing and assigned to an N_Port or NL_Port.

The Port_ID hierarchy includes an 8-bit Domain ID (typically a switch number), an 8-bit Area ID (a port or group of switch ports) and an 8-bit Device ID (typically 00 for N_Ports or for NL_Ports, the Loop Initialization assigned Arbitrated Loop Physical Address (ALPA). The Port_ID of the Source Port (S_ID) and the Port_ID of the Destination Port (D_ID) is used in the Fibre Channel frame header for routing.


[Fibre Channel] A Name_Identifier that is associated with a Fibre Channel port.

port bypass circuit

[Fibre Channel] A circuit that automatically opens and closes a Fibre Channel arbitrated loop so that nodes can be added to or removed from the loop with minimal disruption of operations.

Port bypass circuits are typically found in Fibre Channel hubs and disk enclosures.

port login

[Fibre Channel] The port-to-port login process by which Fibre Channel initiators establish sessions with targets.

Port VF_ID

[Fibre Channel] A configurable VF_ID that is associated with any untagged frame received by a VF capable Multiplexer.


[Computer System] Acronym for Power On Self Test.

post-process data deduplication

[Storage System] Data deduplication performed after the data to be deduplicated has been initially stored.

See inline data deduplication.

power conditioning

[General] The regulation of power supplied to a system so that acceptable ranges of voltage and frequency are maintained.

Power conditioning is sometimes done by a storage subsystem, but may also be an environmental requirement.

Power Distribution Unit (PDU)

[Computer System] An element or device which distributes power to and possibly monitors the power consumption of other devices in a system.

power efficiency

[Computer System] Synonym for electrical efficiency.

Power On Self Test (POST)

[Computer System] A set of internally stored diagnostic programs run by intelligent devices when powered on, that verify the basic integrity of hardware before software is permitted to run on it.

power supply

[Computer System] A component which converts an AC or DC voltage input to one or more DC voltage outputs for the purpose of powering a system or subsystem.

Power supplies may be redundant and hot swappable.

power supply efficiency

[Storage System] The electrical efficiency of a power supply, not including the fan power required to cool it.

In a perfect world, any power required to keep the power supply within specified operating temperature limits would be included in the calculation. In this one, the convention to measure efficiency without it saves much work and controversy.

Power Supply Unit (PSU)

[Computer System] Synonym for power supply.


[Data Security] Acronym for Protection Profile.


[SCSI] Shorthand for PCI Express Queuing Interface.


[Storage System] To cause to appear or to make available.

RAID control software and volume managers present virtual disks to host environments. Synonym for export.


[Data Management] The processes and operations involved in ensuring the ability to read, interpret, authenticate, secure and protect against the loss of data or information throughout its lifecycle.

preservation object

[Long Term Retention] The basic unit of data or information that is preserved by a preservation system.

The Archival Information Package (AIP) defined in Open Archival Information System (OAIS) is an example of a preservation object.

preservation system

[Long Term Retention] A repository that, either as its sole responsibility or as one of multiple responsibilities, undertakes all necessary actions for the long-term preservation of the data or information in its custody.

Primary storage

[Data Management] Data storage device, system, or service used to store data that is accessed frequently by applications.

primitive sequence

[Fibre Channel] In a data stream using 8B/10B encoding, an ordered set transmitted repeatedly and continuously until a specified response is received.

primitive signal

[Fibre Channel] In a data stream using 8B/10B encoding, an ordered set with a special meaning such as an idle or Receiver_Ready (R_RDY).


[Management] [Data Security] Short for security principal.

Priority-based Flow Control (PFC)

[Network] A DCB component that provides a mechanism for link level flow control on a per-priority basis for full-duplex links.

privacy breach

[Data Security] An event that exploits a vulnerability to reveal PII, or creates a loss of control over PII.

private cloud

[Services] Delivery of SaaS, PaaS, IaaS and/or DaaS to a restricted set of customers, usually within a single organization.

Private Clouds are created due to issues of trust.

private key

[Data Security] The cryptographic key in an asymmetric cryptosystem that is not made public.

private key cryptography

[Data Security] An encryption methodology in which the encryptor and decryptor use the same key, which must be kept secret. See symmetric cryptosystem.

private loop

[Fibre Channel] A Fibre Channel arbitrated loop with no fabric attachment.

private loop device

[Fibre Channel] A Fibre Channel arbitrated loop device that does not support fabric login.


[Data Security] A right granted to an individual, a program, or a process. [CNSSI-4009]

privileged user

[Data Security] A user who, by virtue of function or seniority, has been allocated powers within a system that are significantly greater than those available to the majority of users.

Such persons will include, for example, the system administrator(s), storage administrator(s), and network administrator(s) who are responsible for keeping the system available and may need powers to create new user profiles as well as add to or amend the powers and access rights of existing users.

process policy

[Fibre Channel] An error handling policy that allows an N_Port to continue processing data frames following detection of one or more missing frames in a sequence.


[Fibre Channel] A value in the Association_Header that identifies a process or a group of processes within a node.

Communicating processes in different nodes use Process_Associators to address each other. Originating processes have Originator Process_Associators; responding processes have Responder Process_Associators.


[Standards] A proper subset of a standard that supports interoperability across a set of products or in a specific application.

A profile is a vertical slice through a standard containing physical, logical and behavioral elements required for interoperability.

proprietary interconnect
proprietary I/O interconnect

[Storage System] An I/O interconnect (either a host I/O interconnect or a device I/O interconnect) whose transmission characteristics and protocols are the intellectual property of a single vendor, and require the permission of that vendor to be implemented in the products of other vendors.

See open interconnect.

protected space
protected space extent

[Storage System] The storage space available for application data in a physical extent that belongs to a redundancy group.

Protection Profile (PP)

[Data Security] An implementation-independent set of security functional and assurance requirements for a category of IT products that meet specific consumer needs.

PPs are most commonly associated with ISO 15408.


[General] A set of rules that control an interaction between two or more entities in communication with one another, e.g., TCP ports, Fibre Channel FC-4 processes and polite humans.

Rules may specify the formats of a set of communication messages, and in what sequences they are expected to occur.

Protocol Data Unit (PDU)

1. [Network] A single message between two network nodes used for communication.

2. [iSCSI] The term used to describe one iSCSI message sent by either a target or an initiator in an iSCSI connection.


[General] Information regarding an item's source, origin, custody and ownership.


[Computer System] The process of initializing and equipping a system to prepare it to provide services.

Proxy Fabric

[Fibre Channel] In an IFR environment, the remote fabric associated with a Proxy Nx_Port.

Proxy Nx_Port

[Fibre Channel] A role of an Nx_Port in an IFR environment.

From the perspective of a remote (Proxy) Fabric, an Nx_Port assumes the role of a Proxy Nx_Port.


[Computer System] Acronym for Power Supply Unit.

public cloud

[Services] Delivery of SaaS, PaaS, IaaS and/or DaaS to a relatively unrestricted set of customers.

public key

[Data Security] A cryptographic key that is made public for purposes of using asymmetric encryption with an entity that has the private key.

public key cryptography

[Data Security] Synonym for asymmetric cryptography.

Public Key Infrastructure (PKI)

[Data Security] A collection of software, hardware, people and procedures that facilitate secure creation and management of digital certificates.

public loop

[Fibre Channel] A Fibre Channel arbitrated loop with an attachment to a fabric.

public loop device

[Fibre Channel] A Fibre Channel arbitrated loop device that supports fabric login and services.

pull technology

[Computer System] The transmission of information in response to a request for that information.

An example of a pull technology is polling. See push technology.


[Data Security] A method of sanitization that reduces devices or components to fine particles of a specified size.

Pulverization is related to shredding, but usually uses a grinding process as opposed to a cutting process. [ISO/IEC 27040]


1. [Data Security] A class of sanitization that makes recovery infeasible using state of the art laboratory techniques, but which preserves the storage media in a potentially reusable state. [ISO/IEC 27040]

2. [Storage System] The process of returning a solid state storage device to a state in which subsequent writes execute, as closely as possible, as if the device had never been used and does not contain any valid data. See FOB.

push technology

[Computer System] The transmission of information from a source or initiator without a request to the source to send that information.

An example of a push technology is an SNMP trap. See pull technology.