SNIA Online Dictionary

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RADIUS	[Data Security] Acronym for Remote Authentication Dial In User Service.
RAID	[Storage System] Acronym for Redundant Array of Independent Disks.
RAID 0	[Storage System] A data placement policy where consecutive logical blocks of data are uniformly distributed across a set of independent storage devices without offering any form of redundancy. This is commonly referred to as data striping. This form of RAID will encounter data loss with the failure of any storage device in the set.
RAID 00	[Storage System] A data placement policy that creates a RAID 0 stripe set over two or more RAID 0 sets. This is commonly referred to as RAID 0+0. This form of data layout is not fault tolerant; if any storage device fails there will be data loss.
RAID 1	[Storage System] A data placement policy where each logical block of data is stored on more than one independent storage device. This is commonly referred to as mirroring. Data stored using this form of RAID is able to survive a single storage device failure without data loss.
RAID 10	[Storage System] A data placement policy that creates a striped device (RAID 0) over a set of mirrored devices (RAID 1). This is commonly referred to as RAID 1/0. Data stored using this form of RAID is able to survive a single storage device failure in each RAID 1 set without data loss.
RAID 2	[Storage System] A data placement policy in which an error detecting code computed on stripes of data from some independent storage devices is stored on additional independent storage devices. RAID 2 is not widely used.
RAID 3	[Storage System] A data placement policy using parity-based protection where logical bytes of data are uniformly distributed across a set of independent storage devices and the parity is stored on a dedicated independent storage device. Data stored using this form of RAID survives a single storage device failure. If the storage devices use rotating media, they are assumed to be rotationally synchronized, and the data stripe size should be no larger than the exported block size.
RAID 4	[Storage System] A data placement policy using parity-based protection where logical blocks of data are uniformly distributed across a set of independent storage devices and the parity is stored on a dedicated independent storage device. Data stored using this form of RAID is able to survive a single storage device failure without data loss.
RAID 5	[Storage System] A data placement policy using parity-based protection for storing stripes of 'n' logical blocks of data and one logical block of parity across a set of 'n+1' independent storage devices where the parity and data blocks are interleaved across the storage devices. Data stored using this form of RAID is able to survive a single storage device failure without data loss.
RAID 6	[Storage System] A data placement policy using parity-based protection that allows stored data to survive any two storage device failures without data loss.
RAID array	[Storage System] Shorthand for Redundant Array of Independent Disks.
RAID-Z	[Storage System] A form of RAID implemented in the open source ZFS project.
RAID01	[Storage System] A data placement policy that creates a mirrored device (RAID 1) over a set of striped devices (RAID 0). This is commonly referred to as RAID 0+1 or RAID 0/1. Data stored using this form of RAID is able to survive a single RAID 0 data set failure without data loss.
RAID1Triple	[Storage System] A placement policy where each logical block of data is mirrored three times across a set of three independent storage devices. This is commonly referred to as three-way mirroring. This form of RAID can survive two device failures without data loss.
raised floor	[General] An elevated floor providing space for cable runs between equipment cabinets and cold air flow for cooling. Many mainframe systems are designed to intake cool air from the bottom and exhaust heat from the top of a closed cabinet system.
RAM drive	[Storage System] A quantity of host system random access memory (RAM) managed by software and presented to applications as a high-performance drive. RAM drives generally emulate disk I/O functional characteristics, but unless augmented by special hardware to make their contents non-volatile, they cannot tolerate loss of power without losing data. See solid state drive.
random I/O load	[Storage System] An I/O load that consists of random I/Os. The term random I/O is commonly used to denote an I/O load that is not sequential, whether or not the distribution of data locations is indeed random. Random I/O is characteristic of I/O request-intensive applications. See sequential I/O.
random I/Os	[Storage System] A combination of random reads and/or random writes.
random number	[General] A number having properties of randomness or unpredictability. There are three basic classes of random number. Deterministic or pseudorandom numbers are generated by an algorithm that produces a predictable sequence of values from an initial value called a seed. Cryptographically secure random numbers are produced in a sequence that, while deterministic, cannot be feasibly discovered or computed by examination of previous numbers in the sequence. Nondeterministic generators incorporate input from some unpredictable physical source that is outside human control.
random reads	[Storage System] Consecutively issued read requests that do not specify adjacently addressed data.
random relative offset	[Network] A transmission control algorithm that allows frames for a block of data to be transmitted in any order. Each frame of a block of data contains an offset relative to the beginning of that block of data. See relative offset and continuously increasing relative offset.
random writes	[Storage System] Consecutively issued write requests that do not specify adjacently addressed data.
rank	[Storage System] 1. [Storage System] A set of physical disk positions in an enclosure. 2. [Storage System] The set of corresponding target identifiers on all of a controller's device I/O interconnects. 3. [Storage System] Synonym for a stripe in a redundancy group. Because of the diversity of meanings attached to this term, SNIA publications make minimal use of it.
ransomware	[Data Security] A type of malicious software designed to block access to data until funds are paid.
rapid elasticity	[Computer System] Quick scaling of resources and capabilities to meet expansion and contraction of demand. To the consumer, the capabilities available for provisioning often appear to be unlimited and available for purchase in any quantity at any time.
rapid provisioning	[Computer System] Quickly and automatically deploying services in response to requests.
RAS	[Computer System], [Windows] 1. [Computer System] Acronym for reliability, availability, and serviceability. 2. [Windows] Acronym for Remote Access Service.
raw capacity	[Storage System] The total addressable capacity of the storage devices in a storage system.
raw partition	[Storage System] A device partition not managed by a volume manager. The term raw partition is frequently encountered when discussing database systems because some database system vendors recommend volumes or files for underlying database storage, while others recommend direct storage on raw partitions.
raw partition backup	[Data Recovery] A bit-by-bit copy of a partition image. A raw partition backup incorporates no information about the objects contained on the partition, and hence cannot be used for individual object restoration. See disk image backup.
RBAC	[Data Security] Acronym for role-based access control.
RDMA	[Computer System] Acronym for remote direct memory access
read/write head	[Storage System] The magnetic or optical recording element of a disk drive.
ready idle	[Storage System] Synonym for idle.
real time data deduplication	[Storage System] Synonym for inline data deduplication.
rebuild	[Storage System] The regeneration and writing onto one or more replacement devices of all of the data that was on a failed device in a RAID array. In most arrays, a rebuild can occur while applications continue to access the data.
receiver	[Hardware], [Fibre Channel] 1. [Hardware] An interconnect or network device that includes a detector and signal processing electronics. 2. [Hardware] A circuit that converts an optical or electrical media signal to an electrical serial logic signal. 3. [Fibre Channel] The portion of a Link Control Facility dedicated to receiving an encoded bit stream using the rules specified by FC-0.
receptacle	[Network] The stationary half of the interface connector on a transmitter or receiver.
reconstruction	[Storage System] Synonym for rebuilding.
Recorded Volume Serial Number	[Data Recovery] Synonym for media ID.
recovery	[Data Recovery] The recreation of a past operational state of an entire application or computing environment. Recovery is required after an application or computing environment has been destroyed or otherwise rendered unusable. It may include restoration of application data, if that data had been destroyed as well.
Recovery Point Objective	[Data Recovery] The maximum acceptable time period prior to a failure or disaster during which changes to data may be lost as a consequence of recovery. Data changes preceding the failure or disaster by at least this time period are preserved by recovery. Zero is a valid value and is equivalent to a "zero data loss" requirement.
Recovery Time Objective	[Data Recovery] The maximum acceptable time period required to bring one or more applications and associated data back from an outage to a correct operational state.
Redfish	[Management] A DMTF open standard specification and schema that specifies a RESTful interface that utilizes JSON and OData for managing scalable hardware platforms.
Redfish schema	[Management] The representation of Redfish resources and data model using Common Schema Definition Language.
Redfish service	[Management] An OData service that conforms to Redfish.
Redfish service entry point	[Management] A URI through which a particular instance of a Redfish service is accessed.
reduced mode	[Storage System] Synonym for degraded mode.
reduction	[Storage System] The removal of a member disk from a RAID array, placing the array in degraded mode. Reduction most often occurs because of a member drive failure, however, some RAID implementations allow reduction for system management purposes.
redundancy	[General] The inclusion of extra components of a given type in a system (beyond those required by the system to carry out its function) for the purpose of enabling continued operation in the event of a component failure.
redundancy group	[Storage System] A collection of extents organized for the purpose of providing data protection. Within a redundancy group in a storage array, a single type of data protection is employed. All of the usable storage capacity in a redundancy group is protected by check data stored within the group, and no usable storage external to a redundancy group is protected by check data within it.
redundancy group stripe	[Storage System] A set of strips comprising a redundancy group. The check data blocks in a redundancy group stripe protect the protected space in that stripe.
redundancy group stripe depth	[Storage System] The number of blocks in one strip of a redundancy group stripe. In the conventional striped data mapping model, redundancy group stripe depth is the same for all stripes in a redundancy group.
Redundant Array of Independent Devices	[Storage System] A storage array in which part of the physical storage capacity is used to store redundant information about user data stored on the remainder of the storage capacity. The redundant information enables regeneration of user data in the event that one of the array's member disks or the access path to it fails. Although it does not conform to this definition, disk striping is often referred to as RAID 0. The phrase Redundant Array of Independent Devices is adapted from the 1988 SIGMOD paper A Case for Redundant Arrays of Inexpensive Disks. The term was changed to Redundant Array of Independent Disks. In modern systems, RAID techniques are often applied to independent storage devices that implement block storage, including technologies other than disk.
Redundant Array of Independent Disks	[Storage System] Deprecated term for Redundant Array of Independent Devices
Redundant Array of Independent Nodes	[Storage System] A collection of networked server nodes with software that provides and maintains pools of highly available storage capacity.
redundant configuration	[Computer System] A configuration of a system in which failure tolerance is achieved by the presence of redundant instances of all components that are critical to operation.
redundant configuration	[Computer System] A configuration of a system in which failure tolerance is achieved by the presence of redundant instances of all components that are critical to operation.
redundant system	[Computer System] A system in which failure tolerance is achieved by the presence of redundant instances of all components that are critical to operation.
reference data	[Data Management] Synonym for fixed content.
reference information	[Data Management] Synonym for fixed content.
refreshment	[General], [Long-Term Retention] 1. [General] Synonym for beer. 2. [Long-Term Retention] A type of migration where the contents of some media are copied onto newer media of the same type.
regeneration	[Storage System] Recreation of user data from a failed drive in a RAID array using check data and user data from surviving members. Regeneration may be used to recover data from an unrecoverable media error.
registered state change notification	[Fibre Channel] A Fibre Channel function that allows notification to registered nodes if a change occurs to other specified nodes.
rejoin mirror	[Storage System] To bring a split mirror component back into the mirror.
rekeying	[Data Security] Process of updating and redistributing the shared secret key, and optionally, key encryption keys [ISO/IEC 11770-5]. This process is executed by the key distribution center.
relative offset	[General] The offset of a piece of data relative to a reference point.
Remote Access Service	[Windows] A Windows service that provides remote access capabilities to client applications.
Remote Authentication Dial-In User Service	[Data Security] An authentication and accounting protocol used by many Internet Service Providers (ISPs). Information such as username and password is entered when a connection is made. This information is passed to a RADIUS server that verifies the information in order to authorize access to the system. RADIUS is defined in RFC 2865.
remote direct memory access	[Network] A protocol that enables direct memory access over a network.
removable media library	[Backup] Synonym for library.
removable media storage device	[Storage System] A storage device designed so that its storage volumes can be readily removed and inserted. Tapes, DVDs, and optical disks are examples of removable media storage devices.
replacement disk	[Storage System] Synonym for spare disk.
replay attack	[Data Security] An attack in which a valid data transmission is maliciously or fraudulently repeated, either by the originator or by an adversary who intercepts the data and retransmits it.
replica	[Data Recovery] 1. A general term for a copy of a collection of data. See duplicate, point in time copy, snapshot. 2. An image of data usable by one or more applications without an intermediate restore process.
replicate	[Data Recovery] The action of making a replica.
Representational State Transfer	[Services] A specific set of principles for defining, addressing and interacting with resources addressable by URIs. Architectures that follow these principles are said to be RESTful. The principles include: abstraction of state into resources and a uniform set of representations and operations (e.g., HTTP verbs like GET and PUT as the only means to manipulate a resource).
repudiation	[Data Security] The act of a principal in denying, disowning or disavowing an act, event or transaction.
request for comment	[General] A process used to request feedback.
reserved field	[Standards] A field in a data structure set aside for future definition. Some standards prescribe implementation behavior with respect to reserved fields (e.g., originators of data structures containing reserved fields must zero fill them; consumers of data structures containing reserved fields must ignore them, etc.).
resiliency	[Storage System] The ability of a storage subsystem to preserve data integrity and availability of access despite the unavailability of one or more of its storage devices.
resource pooling	[Computer System] Aggregation of a provider's resources to serve multiple consumers using a multitenant model, with physical and virtual resources dynamically assigned and reassigned on demand.
Resource Reservation Protocol	[Management] An IETF protocol for requesting reservation of network bandwidth in advance.
responder	[Fibre Channel], [Storage System] [Storage System] The entity that responds to a request. [Fibre Channel] The Nx-Port that received a frame that caused an Exchange to become open.
Responder Exchange Identifier	[Fibre Channel] An identifier assigned by a responder to identify an Exchange.
REST	[Services] Abbreviation for Representational State Transfer.
restoration	[Data Recovery] Synonym for recovery.
retention period	[Data Management], [Data Recovery], [File System] 1. [Data Recovery] The length of time that a backup copy should be kept. 2. [File System] A property of a file that can be used to implement backup and data migration policies. 3. [Data Management] The length of time a compliance volume or file must be maintained undeleted and unchanged.
retention policy	[Data Management] A policy governing when and for how long a record must be retained by a storage system. This may be a rule that applies to a record or groups or categories of records. The policy may be time or event based.
retimer	[Hardware] A circuit that uses a clock independent of the incoming signal to generate an outbound signal.
return loss	[Hardware] The ratio of the strength of a returned signal to that of the incident signal that caused it. In electrical circuits, return loss is caused by impedance discontinuities. Optical return loss is caused by index of refraction differences.
RFC	[General], [Standards] [General] Shorthand for request for comment. [Standards] A series of documents published by the IETF that are developed by the IETF, the Internet Architecture Board (IAB), and the Internet Research Task Force (IRTF).
risk	[Data Security] The combination of the probability of an event and the significance of its consequences. [ISO Guide 73]. The term "risk" is generally used only when there is at least the possibility of negative consequences. In some situations, risk arises from the possibility of deviation from the expected outcome or event.
risk acceptance	[Data Security] Informed decision to take a particular risk [ISO Guide 73]. Risk acceptance can occur without risk treatment or during the process of risk treatment. Accepted risks are subject to monitoring and review.
risk analysis	[Data Security] Process to comprehend the nature of risk and to determine the level of risk [ISO Guide 73]. Risk analysis provides the basis for risk evaluation and decisions about risk treatment. Risk analysis includes risk estimation.
risk management	[Data Security] Coordinated activities to direct and control an organization with regard to risk [ISO Guide 73].
risk treatment	[Data Security] Process to eliminate risk (3.16) or reduce it to a tolerable level [ISO Guide 73].
robotic media handler	[Storage System] The mechanical component of a library which moves removable media within the library.
RoCE	[Network] RDMA over Converged Ethernet. RoCE V1 is a non-routed protocol and RoCE V2 is a routed protocol. Both were developed by the InfiniBand Trade Association.
role-based access control	[Data Security] An access control method that assigns permissions to roles that reflect the organization and policies of an organization.
rollback to snapshot	[Storage System], [File System] 1. [Storage System] The process of resetting a volume's data to become identical to a snapshot taken of that volume. 2. [File System] In LTFS, the process of modifying the index to match a previous version of the index.
rotational latency	[Storage System] The time interval between the end of a disk seek and the time at which the starting block address specified in the I/O request passes the disk head.
routing function	[Network] A switching entity that forwards packets towards their destination.
row	[Storage System] The set of blocks with corresponding physical extent block addresses in each member disks physical extents. The concept of rows is useful for locking the minimal amount of data during a RAID array update so as to maximize the potential for parallel execution.
RPO	[Data Recovery] Shorthand for Recovery Point Objective.
RSA	[Data Security] A public key algorithm developed by Rivest, Shamir & Adelman.
RSCN	[Fibre Channel] Shorthand for registered state change notification.
RSVP	[Management] Shorthand for Resource Reservation Protocol.
RTO	[Data Recovery] Shorthand for Recovery Time Objective.
run length	[Data Communication] The number of consecutive identical bits in a transmitted signal. For example, the pattern 0011111010 has run lengths of 2, 5, 1, 1, and 1.
running disparity	[Data Communication] In a data stream using 8B/10B encoding, the cumulative disparity (positive or negative) of all previously issued transmission characters.
RVSN	[Data Recovery] Shorthand for Recorded Volume Serial Number.
RX_ID	[Fibre Channel] Abbreviation for Responder Exchange Identifier.