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DAC	[Hardware], [Data Security] 1. [Data Security] Acronym for Discretionary Access Control. 2. [Hardware] Acronym for Digital Analog Converter.
daemon	[Operating System] A long running process on a computer system that services a particular type of request.
DAS	[Storage System] Acronym for Direct Attached Storage.
data	[Computer System] The digital representation of anything in any form.
data at rest	[Data Security] Data stored on stable non-volatile storage. [ISO/IEC 27040].
data authentication	[Legal] The process of substantiating that the data is an accurate representation of what it purports to be. [SWGDE/ SWGIT Glossary]
data availability	[Storage System] The amount of time that data is accessible by applications during those time periods when it is expected to be available, often expressed as a percentage. See availability, high availability.
data breach	[Data Security] A compromise of security that leads to the accidental or unlawful destruction, loss, alteration, unauthorized disclosure of, or access to protected data transmitted, stored or otherwise processed. [ISO/IEC 27040]
Data Center Bridging	[Network] The suite of Ethernet protocol extensions defined for reliable storage transports such as FCoE. DCB includes the following protocols: IEEE 802.1Qau (CN), IEEE 802.1Qaz (ETS and DCBX), and IEEE 802.1Qbb (PFC). A data center bridge implements the above protocols and capabilities for use in the data center.
Data Center Bridging eXchange protocol	[Network] A DCB component for discovery and exchange of DCB information.
data character	[Network] Any transmission character associated by the transmission code with a valid data byte.
data classification	[Data Management] An organization of data into sets for management purposes. A frequent purpose of a classification scheme is to associate service level objectives with sets of data based on their value to the business.
data compression	[General] The process of encoding data to reduce its size. Lossy compression (i.e., compression using a technique in which a portion of the original information is lost) is acceptable for some forms of data (e.g., digital images) in some applications, but for most IT applications, lossless compression (i.e., compression using a technique that preserves the entire content of the original data, and from which the original data can be reconstructed exactly) is required.
data deduplication	[Storage System] The replacement of multiple copies of data, at variable levels of granularity, with references to a shared copy in order to save storage space and/or data transferred. See also inline data deduplication, post-process data deduplication.
data deduplication ratio	[Storage System] A space reduction ratio that includes only the space reduction effects of data deduplication.
data frame	[Fibre Channel] A frame containing information used by an FC-4.
data in flight	[Data Security] Synonym for data in motion.
data in motion	[Data Security] Data being transferred from one location to another [ISO/IEC 27040:2015]. Those transfers typically involve interfaces that are externally accessible and do not include internal transfers (i.e., never exposed to outside of an interface, chip, or device).
data in transit	[Data Security], [Legal] 1.[Data Security] Synonym for data in motion. 2.[Legal] Data in motion across a jurisdictional boundary. Jurisdictions (usually nation states) may have policies and enforcement points that determine whether data may cross their borders.
data in use	[Data Security] Data in the process of being created, retrieved, manipulated, updated, or deleted.
data ingestion	[Data Management] A process for depositing data into a system.
data integrity	[Data Management], [Data Security] [Data Security] The property that data has not been altered or destroyed in an unauthorized manner [ISO 7498-2:1988]. [Data Management] The property that data has not been altered or destroyed, in an unintended manner, due to physical or logical events.
data lake	[Data Management] A large repository for storing data in an unstructured way, in anticipation of future analytics. This term originated in the big data community.
Data Lifecycle Management	[Data Management] The policies, processes, practices, services and tools used to align the business value of data with the most appropriate and cost-effective storage infrastructure from the time data is created through its final disposition. Data is aligned with business requirements through management policies and service levels associated with performance, availability, recoverability, cost, etc. DLM is a subset of ILM.
data management	[Management] The discipline and function of oversight and control of data.
data management services	[Data Management] A set of services that control data from the time it is created until it no longer exists. Data Management services are not in the data path; rather, they provide control or utilize data in the delivery of their services. This includes services such as data movement, data redundancy, and data deletion. Some data management services are managed using the control plane.
data manager	[File System] A function that presents a view of data to applications, and maps that view to an internal representation on a system, subsystem or device. File systems and database management systems are examples of data managers.
data plane	[Computer System] The portion of a system that moves user data. In a storage system the data plane is responsible for storing and retrieving data. Also see control plane.
data portability	[Data Communication] The ability to transfer data with its metadata from one system to another system that preserves meaning.
data preservation	[Data Management] The processes of ensuring data integrity, continued existence, and usability of stored data over a period of time.
data processing unit	[Network] An accelerator element capable of parsing, processing, and transferring data with performance efficiency.A data processing unit (DPU) usually has a set of programmable acceleration engines that offload and improve performance for applications such as AI/ML, security, telecommunications, or storage. DPUs may also be called SmartNICs, IPUs or NAPUs.
data protection	[Data Management] The combination of data integrity, data availability, and confidentiality.
data reliability	[Data Management] The length of the statistically expected continuous span of time over which data stored by a population of identical storage subsystems can be correctly retrieved, expressed as Mean Time to Data Loss (MTDL).
data replication	[Storage System] Continuously maintaining a copy of data–possibly at a remote site–from a volume to provide high availability and redundancy. Data replication may be used for disaster recovery and business continuance.
data repository	[Data Security] Implementation of a collection of data along with data access and control mechanisms, such as search, indexing, storage, retrieval and security. [ISO/IEC 20944-1:2013] EXAMPLE: A repository might support services such as search, indexing, storage, retrieval and security.
data resource domain	[Management] The category of resources that exclusively encompass data management services.
data retention	[Long-Term Retention] Preserving the existence and integrity of data for some period of time or until certain events have transpired.
data service	[Data Management] A set of functions that process data without interpretation. This processing may involve copying, movement, security and/or protection, but not the actual storage of the data.
data shredding	[Data Management] A process for deleting data that is intended to make the data unrecoverable. One such process consists of repeated overwrites of data on the storage media. Data shredding is not generally held to make data completely unrecoverable in the face of modern forensic techniques–that requires physical destruction of the storage media. Forensic techniques, however, do require physical access to the storage media.
Data Storage as a Service	[Services] Typically, Data Storage as a Service (DSaaS) hides limits to scalability, is either self-provisioned or provisionless and is billed based on consumption.
data striping	[Storage System] A disk array data mapping technique in which fixed-length sequences of virtual disk data addresses are mapped to sequences of member disk addresses in a regular rotating pattern. Data stripping is commonly used in RAID implementations.
data transfer capacity	[Computer System] The maximum rate at which data can be transmitted. See data transfer rate.
data transfer device	[SCSI] A removable media storage device in a library. Examples are magnetic disk drives, cartridge tape drives, optical disk drives, and CD-ROM drives.
data transfer rate	[Computer System] The amount of data per unit time actually moved across an interconnect.
Database Management System	[Database] A database management system (DBMS) removes the need for a user or program to manage low level database storage. It also provides security for and assures the integrity of the data it contains. Types of database management systems are relational (table-oriented), network, hierarchical and object oriented.
datagram	[Network] A message sent between two communicating entities for which no explicit acknowledgement is expected. Datagrams are often said to be sent on a best effort basis.
DBMS	[Database] Abbreviation for Database Management System.
DCB	[Network] Acronym for Data Center Bridging.
DDR / DDR2 / DDR3 / DDR4 / DDR5	[Hardware] Acronym for Double Data Rate. The number after the DDR term designates the generation of the memory (e.g., DDR4 is the fourth generation of a DDR bus).
decoding	[Network] Conversion of received transmission characters to valid data bytes and special codes.
decryption	[Data Security] Conversion of encrypted information to plaintext based on the algorithm and key(s) used to encrypt it.
dedicated connection	A communication circuit between two N-Ports maintained by a Fibre Channel fabric. The port resources used by a dedicated connection cannot be used for other purposes during the life of the dedicated connection.
deduplication	[Storage System] See data deduplication.
defense-in-depth	[Data Security] An information assurance strategy integrating people, technology, and operations capabilities to establish multiple security barriers across layers and dimensions of a protected system. [NIST SP 800-53]
degaussing	[Data Security] 1. A procedure that renders data unreadable by applying a strong magnetic field to the media. 2. Applying a degaussing procedure. Degaussing is also called demagnetizing and erasure. Both of these terms are misleading, because in magnetic digital media the individual magnetic domains are not erased or demagnetized, but simply made to line up in the same direction, which eliminates any previous digital structure.
degraded mode	[Storage System] [Storage System] A mode of RAID array operation in which not all of the array's member disks are functioning, but the array as a whole is able to respond to application read and write requests. [Storage System] A mode where redundancy of a storage system is lost impacting its performance and/or functionality while the system is still able to respond to application read and write requests.
delimiter	[Fibre Channel] An ordered set used to indicate a frame boundary.
delta snapshot	[Data Recovery] A type of point in time copy that preserves the state of data at an instant in time by storing only those blocks that are different from an already existing full copy of the data.
delta-based data deduplication	[Storage System] A method of performing data deduplication by storing or transmitting data in the form of differences from a baseline point in time copy. See hash-based data deduplication.
DEN	[Network] Acronym for Directory Enabled Network.
Denial of Service	[Data Security] Prevention of authorized access to a system resource or the delaying of system operations and functions, with resultant loss of availability to authorized users. [ISO/IEC 27033-1:2015]
destination identifier	[Fibre Channel] An address contained in a Fibre Channel frame that identifies the destination of the frame.
destination Nx_Port	[Fibre Channel] The Nx-Port to which a frame is addressed.
device	[Storage System] Synonym for storage device.
device bus	[Storage System] Synonyms for I/O interconnect.
device channel	[Storage System] A channel used to connect storage devices to a host bus adapter or an intelligent controller. The preferred term is I/O interconnect.
device fanout	[Storage System] Synonym for fanout.
device I/O bus	[Storage System] Synonyms for I/O interconnect.
DF_ID	[Fibre Channel] Acronym for destination Fabric_Identifier.
DH-CHAP	[Data Security] Acronym for Diffie-Hellman augmented Challenge Handshake Authentication Protocol.
DHCP	[Network] Acronym for Dynamic Host Control Protocol.
differential	[SCSI] A SCSI electrical signaling technique in which each control and data signal is represented by a voltage differential between two signal lines. Differential signaling can be used over longer distances than the alternative single ended signaling. See single ended (signaling).
differential incremental backup	[Data Recovery] A backup in which data objects modified since the last full backup or incremental backup are copied. To restore data when differential incremental backups are in use, the newest full backup and all differential backups newer than the newest full backup are required. See cumulative incremental backup, full backup.
differential signaling	[Hardware] An electrical signaling technique in which each logical signal is represented by a voltage differential between two signal lines. Differential signaling can be used over longer distances than the alternative single ended signaling.
Differentiated Services	[Management] A protocol defined by the IETF for managing network traffic based on the type of packet or message being transmitted. The Differentiated Services protocol is often abbreviated as DiffServ. DiffServ rules define how a packet flows through a network based on a 6 bit field (the Differentiated Services Code Point) in the IP header. The Differentiated Services Code Point specifies the "per hop behavior" for the packet or message.
Diffie-Hellman	[Data Security] A key agreement protocol that was developed by W. Diffie and M. E. Hellman in allowing two entities to exchange a secret key over an insecure medium without any prior secrets.
Diffie-Hellman augmented Challenge Handshake Authentication Protocol	[Data Security] A password based Authentication and key management protocol that uses the CHAP algorithm (RFC 1994) augmented with an optional Diffie-Hellman algorithm. DH-CHAP provides bidirectional and may provide unidirectional Authentication between a Fibre Channel Initiator and Responder. DH-CHAP is defined by Fibre Channel â€“ Security Protocols - 2 (FC-SP-2).
DiffServ	[Management] Abbreviation for Differentiated Services.
digest	[Data Security] A binary string of some fixed length derived by a computationally efficient function from a binary input string of arbitrary length. A key feature of cryptographic digests is that given a digest, it is computationally infeasible to find another plaintext string that generates the same digest.
Digital Analog Converter	[Hardware] A device that converts a discretely valued (digital) input to a continuously valued (analog) output.
digital archive	[Data Management] A storage repository or service used to secure, retain, and protect digital information and data for periods of time less than that of long-term data retention. A digital archive can be an infrastructure component of a complete digital preservation service, but is not sufficient by itself to accomplish digital preservation, i.e., long-term data retention.
digital forensics	[Legal] The identification, collection, preservation and analysis of digital evidence for use in legal proceedings.
Digital Linear Tape	[Data Recovery] A family of tape device and media technologies.
digital object auditing	[Long-Term Retention] A methodology to verify and detect threats to the validity of digital preservation objects. Digital object auditing is a process of routine periodic testing of stored digital objects, usually using cryptographic techniques, by comparing their previous signatures and time stamps to their current to verify that change, loss of access, or data loss has not occurred.
digital preservation	[Long-Term Retention] Ensuring continued access to, and usability of, digital information and records, especially over long periods of time.
digital preservation object	[Long-Term Retention] A collection of data, metadata and possibly other resources treated as a unit for digital preservation purposes. A preservation object provides the functionality required to assure the future ability to use, secure, interpret, and verify authenticity of the metadata, information, and data in the container and is the foundational element for digital preservation of information and data.
digital preservation service	[Long-Term Retention] A service providing digital preservation. A digital preservation service includes a comprehensive management and curation function that controls its supporting infrastructure, information, data, and storage services in accordance with the requirements of the information objects it manages to accomplish the goals of digital preservation.
digital signature	[Data Security] A cryptographically derived binary string used to assure information authenticity, integrity, and nonrepudiation. Digital signatures can generally be externally verified by entities not in possession of the key used to sign the information. For example, a secure hash of the information encrypted with the originator's private key when an asymmetric cryptosystem is used. Some algorithms that are used in digital signatures cannot be used to encrypt data. (e.g., DSA).
Digital Signature Algorithm	[Data Security] A subset of the Digital Signature Standard that represents a specific public key algorithm that is only used for digital signatures. The secret key used in DSA operates on the message hash generated by SHA-1; to verify a signature, one recomputes the hash of the message, uses the public key to decrypt the signature and then compares the results. This algorithm is obsolete.
Digital Signature Standard	[Data Security] A standard for digital signature that is published by the National Institute of Standards and Technology (NIST) in Federal Information Processing Standard (FIPS) Publication 186-4. DSS specifies DSA as the algorithm for digital signatures and SHA-x for hashing.
DIMM	[Hardware] Acronym for Dual Inline Memory Module.
Direct Attached Storage	[Storage System] A storage device locally connected to a server and dedicated to that server.
direct connected storage	[Storage System] Synonym of direct attach storage.
direct memory access	[Computer System] The ability for an entity to access memory without processing CPU instructions.
direct routing method	[SCSI] A method used by expanders to route connection requests to devices directly attached to that expander, including other expanders.
directory	[Management], [File System] [File System] A mechanism for organizing information. Directories are usually organized hierarchically (i.e., a directory may contain information about files, objects, and other directories) that are used to organize collections of files and other objects for application or human convenience. [File System] A file or other persistent data structure in a file system that contains information about other files. [Management] An LDAP-based repository consisting of class definitions and instances of those classes. Microsoft's Active Directory (AD) and Novell's NetWare Directory Service (NDS) are examples of enterprise-wide LDAP directories.
directory tree	[File System] A collective term for a directory, all of its files, and each of its subdirectories.
Disaster Recovery	[General] The recovery of data, access to data and associated processing after a loss of use of all or part of a data center. This involves not only an essential set of data but also an essential set of all the hardware and software to continue processing of that data and business. Any disaster recovery may involve some amount of down time.
discard policy	[Fibre Channel] An error handling policy that allows an N_Port or NL_Port to discard data frames received following detection of a missing frame in a Sequence.
disconnection	[Fibre Channel] The process of removing a dedicated connection between two N_Ports.
discovery	[General], [Network], [Storage System], [Services], [Legal] [Legal] Process by which each party obtains information held by another party or non-party concerning a matter. [ISO/IEC 27050-1] Discovery is applicable more broadly than to parties in adversarial disputes. Discovery is also the disclosure of hardcopy documents, Electronically Stored Information and tangible objects by an adverse party. In some jurisdictions the term disclosure is used interchangeably with discovery. [General] The process of finding accessible devices, interfaces, and services. [Storage System] The process of finding devices attached to a storage infrastructure. [Network] The process of finding network interfaces in a networking infrastructure. [Services] The process of finding service interfaces.
Discretionary Access Control	[Data Security] A type of access control that allows a principal owning an object to grant or deny access to other principals.
disk	[Storage System] Synonym for disk drive.
disk array	[Storage System] A set of disks from one or more commonly accessible disk subsystems, combined with a body of control software. The control software presents the disks' storage capacity to hosts as one or more virtual disks. Control software is often called firmware or microcode when it runs in a disk controller. Control software that runs in a host computer is usually called a volume manager.
disk cache	[Storage System] [Storage System] A cache that resides within a disk. [Storage System] A cache that resides in a controller or host. The primary purpose of a disk cache is to improve disk or disk array I/O performance. See controller cache, host cache.
disk drive	[Storage System] A non-volatile, randomly addressable, re-writable data storage device made up of one or more rotating platters. This definition includes rotating magnetic and optical disks.
disk image backup	[Data Recovery] A backup consisting of a copy of each of the blocks comprising the usable storage area of a storage device.
disk striping	[Storage System] Deprecated synonym for data striping.
disk subsystem	[Storage System] A storage subsystem that supports only disks.
disparity	[Network] For a data stream using 8B/10B encoding, the difference between the number of ones and the number of zeros in a transmission character.
disposition	[Legal] Range of processes associated with implementing records retention, destruction or transfer decisions that are documented in disposition authorities or other instruments. [ISO 15489-1:2016]
disposition policy	[Data Management] A policy that defines when lifecycle deletion should occur, and/or what actions to perform.
Distributed FCF	[Fibre Channel] Synonym for Distributed Switch.
Distributed Switch	[Fibre Channel] A set of FCDFs associated with at least one Controlling Switch that controls the operations of the set of FCDFs.
DLM	[Data Management] Acronym for Data Lifecycle Management.
DLT	[Storage System] Acronym for Digital Linear Tape.
DMA	[Computer System] Shorthand for direct memory access.
DMTF	[Management] An industry organization that develops management standards for computer system and enterprise environments. DMTF standards include CIM and Redfish. The DMTF web site is www.dmtf.org.
DNS	[Network] Acronym for Domain Name Service.
Document Type Definition	[Standards] In XML, a specification of the permissible tags or "markup codes" in a document, and their meanings. XML tags are delimited by the characters, "<" and ">". When a Document Type Definition (DTD) is available for a document, a universal reader (program) can parse the document and display or print it.
domain	[Network], [Fibre Channel], [NVMe], [Computer System] [Computer System] A shared user authorization database that contains users, groups, and their security policies. [Fibre Channel] The portion of the Fibre Channel address identifier that represents the highest level in the three-level addressing hierarchy. A domain typically is associated with a single Fibre Channel Switch. [Network] A set of interconnected network elements and addresses that are administered together and that may communicate. [NVMe] The smallest indivisible unit of an NVM subsystem that has a common state.
domain controller	[Fibre Channel], [Operating System] [Operating System] A Windows or Linux server that contains a copy of a user account database. A domain may contain zero or more backup domain controllers and contains a primary domain controller. [Fibre Channel] The control function addressable by an N_Port attached to a Switch using the Domain Controller address identifier of 0xFFFCnn, where nn is the Domain Controller being accessed.
Domain Name Service	[Network] A computer program that converts between IP addresses and symbolic names for nodes on a network in a standard way. Domain Name Service (DNS) is defined by IETF RFC 1035. Most operating systems include a version of DNS.
DoS	[Data Security] Acronym for Denial of Service.
double buffering	[Computer System] {Historical} A technique used to increase data transfer rate by keeping two I/O requests outstanding.
Double Data Rate	[Hardware] A type of bus used to connect a memory DIMM to a CPU.
DPU	[Network] Shorthand for data processing unit
DR	[General] Acronym for Disaster Recovery.
DRAM	[Hardware] Acronym for Dynamic Random Access Memory.
drive	[Storage System] Synonym for storage element (e.g., disk drive, solid state drive, or tape drive).
drive letter	[Windows] A single letter of the alphabet by which applications and users identify a partition or physical or virtual disk to the Windows operating system.
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. Drivers manage communication and data transfer between applications and devices.
DSA	[Data Security] Acronym for Digital Signature Algorithm.
DSaaS	[Services] Acronym for Data Storage as a Service.
DSS	[Data Security] Acronym for Digital Signature Standard.
DTD	[General] Acronym for Document Type Definition.
dual active	[Computer System] Synonym for active-active.
Dual Inline Memory Module	[Hardware] A set of random access memory integrated circuits or chips mounted on a circuit board, providing a 64-bit or greater data path using connectors on both sides of a single card edge. Abbreviated as DIMM.
dual parity	[Storage System] A synonym for RAID 6.
due care	[Data Security] The responsibility that managers and their organizations have a duty to provide for information security to ensure that the type of control, the cost of control, and the deployment of control are appropriate for the system being managed. [NIST SP 800-30]
duplicate	[Computer System], [Data Management] [Data Management] A general term for a copy of a collection of data, including point in time copies. [Data Management] The action of making a copy of a collection of data. See replicate, snapshot. [Computer System] Any redundant component in a system.
duplicate data	[Storage System] Data that is redundant with data that is already in a dataset or I/O stream.
Dynamic Host Control Protocol	[Network] An Internet protocol that allows nodes to dynamically acquire ("lease") network addresses for periods of time. Dynamic Host Control Protocol (DHCP) simplifies the administration of networks by avoiding the need to pre-configure nodes.
dynamic mapping	[Storage System] A form of mapping in which the correspondence between addresses in the two address spaces can change over time. See algorithmic mapping, tabular mapping.
Dynamic Random Access Memory	[Hardware] Byte-addressable computer memory that requires periodic refreshing.
D_ID	[Fibre Channel] A three-byte field that contains the address identifier of the destination Nx_Port.