I_T nexus

[SCSI] A relationship specified in SAM-2 between a SCSI Initiator Port and a SCSI Target Port.


[Services] Acronym for Infrastructure as a Service.


[Network] Acronym for Internet Control Message Protocol.


[Storage System] Acronym for Integrated Drive Electronics.


[General] A property of an operation in which the same result is obtained no matter how many times the operation is performed.

In an environment with a single writer, writing a block of data to a disk is an idempotent operation, whereas writing a block of data to a tape is not, because writing a block of data twice to the same tape results in two adjacent copies of the block.


[Data Security] The process of determining the unique identity of an entity.


[Data Security] Representation of an actual user (or application or service or device).

An example is the assignment of the user name joej (the identity) to represent the human user Joe Jones for purposes of authentication and authorization.


[Storage System] A state in which a storage system is serving no user-initiated I/O requests, but is ready to service them upon arrival with normal latency.

Storage systems may perform extensive system-initiated I/O during idle periods as they execute routine background housekeeping tasks.

idle power

[Energy] The power consumption of a system when powered on but with no active workload.

Idle word

[Fibre Channel] In a data stream using 8B10B encoding, an ordered set of four transmission characters normally transmitted between frames to indicate that a fibre channel network is idle.


[Data Security] Acronym for Intrusion Detection System.


[Network] [Standards] Acronym for Internet Engineering Task Force.


[Storage System] A gateway-to-gateway protocol that provides fibre channel fabric services to fibre channel devices over a TCP/IP network.

ignored (field)

[Fibre Channel] A field that is not interpreted by its receiver.


[Network] [Data Security] Acronym for Internet Key Exchange.


[iSCSI] Acronym for iSCSI Management API.


[Data Management] Acronym for Information Lifecycle Management.

implicit addressing

[Storage System] A form of addressing usually used with tapes in which the data’s address is inferred from the form of the access request.

Tape commands that do not include an explicit block address but implicitly specify the next or previous block from the current tape position, from which the block address must be inferred by the device. See explicit addressing.

import/export element

[SCSI] Synonym for entry/exit slot.


[Data Recovery] Acronym for Incremental Mirror Resynchronization.

in-band (transmission)

[Network] [Fibre Channel] Transmission of a separate data stream, such as management information, over the same medium as the primary data stream.

See out-of-band.

in-band data deduplication

[Storage System] Deprecated synonym for inline data deduplication.

in-band virtualization

[Computer System] Virtualization functions or services that are in the data path.

In a system that implements in-band virtualization, virtualization services such as address mapping are performed by the same functional components used to read or write data. See out-of-band virtualization


[Data Security] An occurrence that actually or potentially jeopardizes the confidentiality, integrity, or availability of an information system or the information the system processes, stores, or transmits or that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies. [NIST FIPS 200]


[Data Security] A method of sanitization that reduces a storage device or element to ash, in an approved facility. [ISO/IEC 27040]


[Standards] Shorthand for International Committee for Information Technology Standards.

INCITS is one of about 100 standards organizations accredited by ANSI to prepare national standards and make recommendations to ANSI concerning international standards. INCITS assigns technical committees to prepare standards associated with information technology, including JPEG, computer security, biometric information, SCSI (Technical Committee T10), Fibre Channel (Technical Committee T11), and many more.


[SCSI] [Standards] The INCITS SCSI Storage Interfaces Technical Committee (INCITS TC T10).

The INCITS T10 Technical Committee is the standards development committee accredited by INCITS to develop SCSI standards for communication between from host devices (initiators) to storage device controllers (targets).


[Fibre Channel] [Standards] The INCITS Fibre Channel Interfaces Technical Committee (INCITS TC T11).

The INCITS T11 Technical Committee is the standards development committee accredited by INCITS to develop standards related to Fibre Channel, related serial storage interfaces, and certain storage management interfaces.

incremental backup

[Data Recovery] Any backup in which only data objects modified since the time of some previous backup are copied.

Incremental backup is a collective term for cumulative incremental backups and differential incremental backups. See cumulative incremental backup, differential incremental backup, full backup.

incremental mirror resynchronization
incremental resynchronization

[Data Recovery] A technique for reducing the time required to synchronize a split mirror with the set of storage devices from which it was split.

Incremental mirror resynchronization requires that a list of changes to the original set of data since moment of splitting be kept. When the split mirror is rejoined to its original set of volumes, only the data items identified in the list are copied from the original to the split mirror (rather than the entire contents of the devices).

independent access array

[Storage System] A disk array whose data mapping is such that different member disks can execute multiple application I/O requests concurrently.

See parallel access array.


[Computer System] A interconnect between computer system(s) and computer system component(s).

This includes computer system to computer system connectivity and computer system component to computer system component connectivity.

infinite buffer

[Fibre Channel] A term indicating that at the FC-2 level, the amount of buffering available at the Sequence Recipient is assumed to be unlimited.

Buffer overrun must be prevented by each ULP by choosing an appropriate amount of buffering per sequence based on its maximum transfer unit size.


[Data Management] Data that is interpreted within a context such as an application or a process.

information assurance

[Data Security] Measures that protect and defend information and information systems by ensuring their availability, integrity, authentication, confidentiality, and nonrepudiation.

Information assurance encompasses system reliability and strategic risk management, and includes providing for restoration of information systems using protection, detection, and reaction capabilities.

information category

[Fibre Channel] A frame header field indicating the category to which the frame payload belongs (e.g., Solicited Data, Unsolicited Data, Solicited Control and Unsolicited Control).

Information Lifecycle Management (ILM)

[Data Management] The policies, processes, practices, services and tools used to align the business value of information with the most appropriate and cost-effective infrastructure from the time information is created through its final disposition.

Information is aligned with business requirements through management policies and service levels associated with applications, metadata and data.

information management

[Data Management] The discipline and function of oversight and control of information resources.

information management services

[Data Management] The processes associated with managing information as it progresses through various lifecycle states associated with a Business Process.

These services exploit information about data content and relationships in making decisions. Examples include records management and content management applications.

information model

[Data Management] A repository-independent definition of entities (i.e., objects) and the relationships and interactions between these entities.

The CIM schemas are an example of an information model. An information model differs from a data model, which is repository-specific.

information resource domain

[Management] The category of resources that exclusively encompass information services.

information security

[Data Security] Preservation of the confidentiality, integrity and availability of information.

[ISO/IEC 27000]

information service

[Management] A set of functions that treat data within an interpretation context.

information system

[Data Security] The entire infrastructure, organization, personnel and components for the collection, processing, storage, transmission, display, dissemination and disposition of information.

Information Technology (IT)

[General] All aspects of information creation, access, use, storage, transport and management.

The term Information Technology addresses all aspects of computer and storage systems, networks, users and software in an enterprise.

Information Unit (IU)

1. [Fibre Channel] An related collection of data specified by FC-4 to be transferred as a single FC-2 sequence.

2. [SCSI] A delimited and sequenced set of information in a format appropriate for transport by the service delivery subsystem.

A SCSI IU may contain a command, data, response, or task management request.

infrastructure-based virtualization

[Computer System] Virtualization implemented in the storage fabric, in separate devices designed for the purpose, or in network devices.

Examples are separate devices or additional functions in existing devices that aggregate multiple individual file system appliances or block storage subsystems into one such virtual service, functions providing transparent block or file system mirroring functions, or functions that provide new security or management services.

Infrastructure as a Service (IaaS)

[Services] Delivery over a network of an appropriately configured virtual computing environment, based on a request for a given service level.

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

ingress Routing Function role

[Fibre Channel] A process within a Routing Function that translates the D_ID, translates embedded N_Port_IDs and stores the Exchange context if needed, adds the IFR_Header and Enc_Header if needed, and then forwards the frame to the next hop Routing Function or Egress Routing Function.

inherent cost

[Computer System] The cost of a system expressed in terms of the number and type of components it contains.

The concept of inherent cost allows technology-based comparisons of disk subsystem alternatives by expressing cost in terms of number of disks, ports, modules, fans, power supplies, cabinets, etc. Because it is inexpensively reproducible, software is generally assumed to have negligible inherent cost.

initial relative offset

[Fibre Channel] The relative offset of the block or sub-block transmitted by the first frame in a sequence, specified by an upper layer protocol.

The initial relative offset need not be zero.


1. [Fibre Channel] The startup and initial configuration of a device, element, system, piece of software or network.

2. [Fibre Channel] For FC-1, the period beginning with power on and continuing until the transmitter and receiver at that level become operational.


1. [Computer System] The system component that originates an I/O command over an I/O interconnect.

2. [SCSI] The endpoint that originates a SCSI I/O command sequence.

I/O adapters, network interface cards, and intelligent I/O interconnect control ASICs are typical initiators. See LUN, originator, target, target port identifier.

initiator NVMe_Port

[Fibre Channel] NVMe_Port which is the NVM host port for an NVMeoFC association.

initiator port identifier

[SCSI] The interconnect address of an initiator.

Initiator Session Identifier (ISID)

[iSCSI] The unique identifier that an initiator assigns to its end point of the session.

When combined with the iSCSI Initiator Name, the Initiator Session Identifier provides a worldwide unique name for its SCSI Initiator Port.

inline data deduplication

[Storage System] Data deduplication performed before writing the deduplicated data.

See post-process data deduplication


[File System] A persistent data structure in a UNIX or UNIX-like file system that describes the location of some or all of the disk blocks allocated to the file.


[General] The creation of an instance of a class or object oriented abstraction.

Integrated Drive Electronics (IDE)

[Computer System] A type of hardware interface widely used to connect hard disks, CD-ROMs and tape drives to a PC, but also used in other systems.

The IDE interface is officially known as the ATA specification.


[Data Security] Property of protecting the accuracy and completeness of assets.

[ISO/IEC 27000]

intelligent controller

[Storage System] Synonym for storage controller.

intelligent device

[Computer System] A computer, storage controller, storage device, or appliance.

Intelligent Peripheral Interface (IPI)

[Network] A high-performance standards-based I/O interconnect.


[Fibre Channel] The entire interconnection of Fabrics and Inter-Fabric Routers.

Inter-Fabric Router

[Fibre Channel] A device that performs Inter-Fabric Routing and consists of a Routing Function, Translate Domain switches, and Front Domain switches.

Inter-Fabric Routing

[Fibre Channel] The process of forwarding frames through a specific Routing Function, including the translation of N_Port_IDs.


[Computer System] A physical facility by which system elements and devices are connected together and through which they can communicate with each other.

I/O buses and networks are both interconnects.

interface connector

[Fibre Channel] An optical or electrical connector that connects the media to the Fibre Channel transmitter or receiver.

An interface connector consists of both a receptacle and a plug.

Intermediate Routing Function

[Fibre Channel] A process within a Routing Function that validates the frame headers, updates the IFR_Header, removes and adds a new Enc_Header, then forwards the frame to the next hop Routing Function.


[Fibre Channel] A Fibre Channel class of service that provides a full bandwidth dedicated Class 1 connection, but allows connectionless Class 2 and Class 3 traffic to share the link during intervals when bandwidth is unused.

International Organization for Standardization (ISO)

[Standards] A worldwide federation of national standards bodies from more than 145 countries; a non-governmental organization whose work results in international agreements that are published as International Standards and other types of ISO documents.

Internet Control Message Protocol (ICMP)

[Network] A control protocol strongly related to IP and TCP, and used to convey a variety of control and error indications.

Internet Engineering Task Force (IETF)

[Network] [Data Security] [Standards] A large open international community of network designers, operators, vendors, and researchers concerned with evolution and smooth operation of the Internet.

The IETF is the standards body responsible for Internet standards called RFCs, including SNMP, TCP/IP and policy for QoS. The IETF has a web site atwww.ietf.org.

Internet Key Exchange (IKE)

[Network] [Data Security] A protocol specified by the IETF that performs mutual authentication between two parties and establishes an IKE Security Association (SA) that includes shared secret information that can be used to efficiently establish SAs for Encapsulating Security Payload (ESP) or Authentication Header (AH) and a set of cryptographic algorithms to be used by the SAs to protect the traffic that they carry.

IKEv2 is defined in RFC-4306.

IKE Version 2 (IKEv2) is not compatible with Version 1.

Internet Protocol (IP)

[Network] A protocol that provides connectionless best effort delivery of datagrams across heterogeneous physical networks.


Internet Small Computer Systems Interface (iSCSI)

[Storage System] A transport protocol that provides for the SCSI protocol to be carried over a TCP based IP network, standardized by the Internet Engineering Task Force and described in RFC 3720.

Internet Storage Name Service (iSNS)

[iSCSI] A protocol and mechanism for intelligent discovery of storage devices in an IP network.


[Computer System] The ability of systems to work with or use data and protocols from other systems.


[Computer System] A hardware or software signal that causes a computer to stop executing its instruction stream and switch to another stream.

Software interrupts are triggered by application or other programs. Hardware interrupts are caused by external events, to notify software so it can deal with the events. The ticking of a clock, completion or reception of a transmission on an I/O interconnect or network, application attempts to execute invalid instructions or reference data for which they do not have access rights, and failure of some aspect of the computer hardware itself are all common causes of hardware interrupts.

interrupt switch

[Computer System] A human-activated switch present on some intelligent devices that is used to generate interrupts.

Interrupt switches are usually used for debugging purposes.

intracabinet specification

[Fibre Channel] A Fibre Channel specification for copper cabling that allows up to 13m total cable length within a single enclosure, which may contain multiple devices.


[Data Security] A deliberate or accidental set of events that potentially causes unauthorized access to, activity against, and/or activity in, an information technology (IT) system.

intrusion detection

[Data Security] The process of identifying that an intrusion has been attempted, is occurring, or has occurred.

Intrusion Detection System (IDS)

[Data Security] A technical system that is used to identify and respond to intrusions in IT systems.


[Computer System] Shorthand for input/output.

I/O is the process of moving data between a computer system’s main memory and an external device or interface such as a storage device, display, printer, or network connected to other computer systems. This encompasses reading, or moving data into a computer system’s memory, and writing, or moving data from a computer system’s memory to another location.

I/O adapter

[Computer System] An adapter that converts between the timing and protocol requirements of a system's memory bus and those of an I/O interconnect or network.

In the context of storage subsystems, I/O adapters are contrasted with embedded storage controllers, that not only adapt between buses and interconnects, but also perform transformations such as device fan-out, data caching, and RAID. host bus adapters (HBAs) and Ethernet NICs are types of I/O adapters.

I/O bottleneck

[Computer System] Any resource in the I/O path (e.g., device driver, host bus adapter, I/O interconnect, intelligent controller, or disk) whose performance limits the performance of a storage subsystem as a whole.

I/O bus

[Computer System] Synonym for I/O interconnect.

I/O device

[Computer System] Synonym for I/O adapter.

I/O driver

[Computer System] A host computer software component (usually part of an operating system) whose function is to control the operation of peripheral controllers or adapters attached to the host computer.

I/O drivers manage communication and data transfer between applications and I/O devices, using host bus adapters as agents. In some cases, drivers participate in data transfer, although this is rare with disk and tape drivers, since most host bus adapters and controllers contain specialized hardware to perform data transfers.

I/O intensity

[Computer System] A characterization of applications that describes how strongly their performance depends on the performance of the I/O subsystem that provides their I/O services.

I/O intensive applications may be either data transfer intensive or I/O request intensive or both.

I/O interconnect

[Computer System] Any path used to transfer data and control information between components of an I/O subsystem.

An I/O interconnect consists of wiring (either cable or backplane), connectors, and all associated electrical drivers, receivers, transducers, and other required electronic components. I/O interconnects are typically optimized for the transfer of data, and tend to support more restricted configurations than networks. See channel, device channel, network.

I/O load

[Computer System] A sequence of I/O requests made to an I/O subsystem.

The requests that comprise an I/O load include both user I/O and host overhead I/O, such as swapping, paging, and file system activity.

I/O load balancing

[Computer System] Synonym for load balancing.

I/O operation

[Computer System] A read, write, or control function performed to, from or within a computer system.

See I/O request.

I/O power efficiency

1. [Storage System] The ratio of maximum IOPS deliverable by a system, to the input power required to deliver those IOPS.

2. [Storage System] The ratio of maximum bandwidth readable or writable by a system, to the input power required to achieve that bandwidth.

I/O request

[Computer System] A request by an application to read or write a specified amount of data.

In the context of real and virtual disks, I/O requests specify the transfer of a number of blocks of data between consecutive disk block addresses and contiguous memory locations. See I/O operation.

I/O subsystem

[Computer System] A collective term for the set of devices and software components that operate together to provide data transfer services.

A storage subsystem is one type of I/O subsystem.



[Storage System] Shorthand for I/O Operations per second.

IOPs can also be the plural of IOP (short for I/O operation), depending on context.


[Energy] Input/Output Operations per Second per Watt.

IOPS/W is a metric for evaluating storage I/O performance per unit of power.


[Network] Acronym for Internet Protocol.


[iSCSI] Block-level Storage Area Networks over TCP/IP using the iSCSI protocol.

IP Security (IPsec)

[Network] [Data Security] A suite of cryptographic algorithms, protocols and procedures used to protect information, authenticate communications, control access, and provide non-repudiation at the IP layer.

The two key protocols in IPsec are the Authentication Header (AH) and Encapsulating Security Payload (ESP) protocols.

IP Storage

[iSCSI] Storage Networking over TCP/IP networks.

IP Storage includes block-level SAN solutions using iSCSI, iFCP and FCIP protocols as well as file-level NAS solutions using protocols such as CIFS and NFS.


[Computer System] Acronym for Intelligent Peripheral Interface.


[Network] [Data Security] Shorthand for IP Security.


[Storage System] Acronym for Internet Small Computer Systems Interface.

iSCSI device

[iSCSI] A SCSI Device using an iSCSI service delivery subsystem, in other words an iSCSI-specific transport mechanism for SCSI commands and responses (information units).

iSCSI initiator name

[iSCSI] The worldwide unique name of an iSCSI initiator.

iSCSI initiator node

[iSCSI] Another name for the iSCSI initiator; an iSCSI Node within the iSCSI Client Network Entity.

iSCSI initiator port

[iSCSI] Another name for a SCSI Initiator Port used for iSCSI.

iSCSI layer

[iSCSI] The layer that builds/receives iSCSI PDUs and relays/receives them to/from one or more TCP connections that form an iSCSI session.

iSCSI Management API (IMA)

[iSCSI] A specification for a C language based API for managing iSCSI capable HBAs and NICs, along with the device drivers that control them.

iSCSI name

[iSCSI] The name of an iSCSI initiator or iSCSI target.

iSCSI network entity

[iSCSI] A device or gateway that is accessible from the IP network and has one or more iSCSI Network Portals.

iSCSI Network Portal

[iSCSI] A component of an iSCSI Network Entity that has a TCP/IP address and can be used by a node within that entity for connections to another iSCSI node.

An Initiator iSCSI Network Portal is identified by its IP address. A target iSCSI Network Portal is identified by its IP address and listening TCP port.

iSCSI Node

[iSCSI] A single iSCSI initiator or iSCSI target.

iSCSI Portal Group

[iSCSI] A set of iSCSI Network Portals within an iSCSI Node.

When a session has multiple connections, all connections in a session must use the portals in a single iSCSI Portal Group.

iSCSI Portal Group Tag

[iSCSI] A tag identifying all portals in an iSCSI Portal Group within an iSCSI Node.

All portals in the group have the same iSCSI Portal Group Tag.


[iSCSI] Block-level Storage Area Networks over TCP/IP using the iSCSI protocol.

iSCSI Session

[iSCSI] The top level relationship between a specific initiator and target, equivalent to the I_T nexus.

A session can contain one or more connections.

iSCSI Session Identifier (ISID)

[iSCSI] A unique identifier for a session between an iSCSI initiator and target.

iSCSI Target Name

[iSCSI] The worldwide unique name of an iSCSI target.

iSCSI Target Node

[iSCSI] Another name for the iSCSI target, i.e., an iSCSI Node within the iSCSI Server Network Entity.

iSCSI Target Port

[iSCSI] Another name for a SCSI Target Port used for iSCSI.


[iSCSI] Acronym for Initiator Session Identifier.


[iSCSI] Acronym for Internet Storage Name Service.

iSNS Discovery Domain

[iSNS] Grouping of storage nodes for facilitating discovery and login control of these nodes.


[Standards] Acronym for International Organization for Standardization.


[General] Acronym for Information Technology.

IT security

[Data Security] All aspects related to defining, achieving, and maintaining confidentiality, integrity, availability, non-repudiation, accountability, authenticity, and reliability of information assets. [ISO/IEC 1335]


[General] Shorthand for Information Unit.