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backup	[Data Recovery] 1. A collection of data stored on (usually removable) non-volatile storage media for purposes of recovery in case the original copy of data is lost or becomes inaccessible; also called a backup copy or replica. To be useful for recovery, a backup must be made by copying the source data image when it is in a consistent state. 2. The act of creating a backup. See archive.
backup client	[Data Recovery] A computer system containing online data to be backed up.
backup copy	[Data Recovery] A collection of data stored on (usually removable) non-volatile storage media for purposes of recovery in case the original copy of data is lost or becomes inaccessible; also called a backup or replica.
backup manager	[Data Recovery] An application program whose purpose is to schedule and manage backup operations.
backup policy	[Data Recovery] Rules for how and when backup should be performed. The policy includes which data is to be backed up, the schedule on which backups should occur, which devices and media are eligible to receive the backups, how many copies are to be made, and actions to be performed if a backup does not succeed.
Backup to Disk	[Data Recovery] Backup onto disk drive(s).
Backup to Tape	[Data Recovery] Backup onto tape media.
backup window	[Data Recovery] An interval of time during which a set of data can be backed up without affecting applications that use the data.
backup window duration	[Data Recovery] The amount of time required to create a backup. For example, if a backup uses different resources (storage devices, I/O paths, processing power) than an application, as is common with split mirror point-in-time copies, then the backup window duration is the time required to create the image. If an online backup shares resources with the applications using the data, as is common with copy-on-write point in time copies, the backup window duration may be increased due to resource contention. For an offline backup, the backup window duration is the time during which applications are not allowed to modify the data while the backup operation completes.
Bandwidth	[General], [Data Communication] 1. The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation. 2. A deprecated synonym for data transfer capacity that is often incorrectly used to refer to throughput.
bandwidth-length product	[Network] A figure of merit for optical fiber, usually expressed as MHzkilometer. As an example, a Fibre Channel link operating at 1 Gb/s using a fiber with a bandwidth-length product of 500 MHzkilometer will support a link distance of approximately 500 meters.
baud	[Network] The maximum rate of signal state changes per second on a communications circuit. If each signal state change corresponds to a code bit, then the baud rate and the bit rate are the same. It is also possible for signal state changes to correspond to more than one code bit, so the baud rate may be lower than the code bit rate.
BB_credit	[Fibre Channel] Synonym for buffer-to-buffer credit.
BCP	[General] Acronym for Best Current Practice.
beginning running disparity	[Fibre Channel] For a data stream using 8B/10B encoding, the running disparity present at a transmitter or receiver when an ordered set is initiated.
BER	[Network], [Storage System] Acronym for Bit Error Rate.
Berkeley RAID Levels	[Storage System] A classification of disk array data protection and mapping techniques developed by Garth Gibson, Randy Katz, and David Patterson in papers written while they were performing research into I/O subsystems at the University of California at Berkeley. There are seven Berkeley RAID Levels, usually referred to by the names RAID Level 0 through RAID Level 6. See RAID 0, RAID 1, RAID 2, RAID 3, RAID 4, RAID 5, RAID 6. Many other levels such as RAID 10, RAID 50 and so on have since been proposed.
Best Current Practice	[General] A recommendation for what is currently believed to be the best manner of proceeding.
best effort	[Network] A class of service that does not guarantee delivery of packets, frames, or datagrams, but for which the network, fabric, or interconnect makes every reasonable delivery effort.
bidirectional authentication	[Data Security] Synonym for mutual authentication.
big data	[Computer System] A characterization of datasets that are too large to be efficiently processed in their entirety by the most powerful standard computational platforms available.
big endian	[Computer System] A format for the storage and transmission of binary data in which the most significant bits are stored at the numerically lowest addresses, or are transmitted first on a serial link.
BIOS	[Computer System] A program that resides in programmable, non-volatile memory on a computer and that is responsible for booting that computer and performing certain operating system independent I/O operations. Standard BIOS interrupts are defined to allow access to the computer's disk, video and other hardware components (for example, INT13 for disk access).
bit	[Computer System] A binary digit.
bit error rate	[Network], [Storage System] The probability that a transmitted bit will be erroneously received at the point of measurement. The BER at a measurement point is determined by counting the number of bits in error at that measurement point and dividing by the total number of bits in the transmission. BER is typically expressed as a negative power of 10.
bit synchronization	[Data Communication] The process by which the receiver of a serial communication establishes its clocking used to locate code bits in a received data stream.
blade system	[Computer System] A computer or storage system composed of a chassis that provides power, cooling and other common infrastructure, and one or more removable server or storage units, usually called blades. Blade systems are designed as a scalable solution to efficiently package and operate multiple processing or storage units in a single enclosure, and are designed for technicians to be able to easily add or replace hot-swappable boards in the field.
blanking plate	[General], [Energy] A solid plate that mounts over unused slots to maintain efficient air flow through components.
blind mating	[Hardware] The ability of pairs of components to be connected without the connection points being visible. Blind mating is usually accomplished by mechanical guides (e.g., slots and rails) on the components.
block	[Storage System] 1. A unit in which data is stored and retrieved on storage media. [Fibre Channel] 2. A unit of application data from a single information category that is transferred within a single sequence.
block addressing	[Storage System] A form of addressing data on storage media where units (blocks) of data are identified by integers that are typically sequential. See C-H-S addressing.
block cipher	[Data Security] A symmetric encryption algorithm that operates on a block of plaintext, i.e., a string of bits of a defined length, to yield a block of ciphertext. [ISO/IEC 18033-1:2015]
block cipher mode of operation	[Data Security] Algorithm that uses a block cipher to provide an information service such as confidentiality or authenticity [ISO/TS 21219-24:2017]
block services	[Storage System] A subsystem that provides block level access to storage for other systems or other layers of the same system. See block.
block storage	[Storage System] A method of storing data in blocks. Disk devices typically store data in fixed size blocks (e.g., 512 byte blocks, or 4,096 byte blocks). Tape devices may provide fixed size blocks or variable sized blocks. The arrangement of those blocks into files occurs using a host file system. Various storage protocols (e.g., SCSI, SATA, FC, iSCSI, RDMA) may be used to access the data in those blocks. Ssee File storage
block virtualization	[Storage System] The act of applying virtualization to a block based (storage) service for the purpose of providing a new aggregated, higher level (e.g., richer, simpler, more secure) block service to clients. Block virtualization functions can be nested. A disk drive, RAID system or volume manager all perform some form of block address to (different) block address mapping or aggregation. See file virtualization.
Blocking	[Computer System] A property of an operation that it may stop and wait for other operations to occur. For example, an operation on file 1 blocks (i.e., stops and waits) for another operation on file 1 to complete.
BNC	[Network] A type of coaxial cable connector formerly used in Ethernet applications; the specification is contained in EIA/TIA 403-A and MIL-C-39012.
bootstrapping	[Computer System] The process of loading Operating System code from a disk or other storage device into a computer's memory and preparing it to run. Bootstrapping typically occurs in steps, starting with a very simple program (BIOS) that initializes the computer's hardware and reads a sequence of data blocks from a fixed location on a pre-determined disk, into a fixed memory location. The data thus read is the code for the next stage of bootstrapping, usually an operating system loader. The loader completes the hardware setup and results in an executing operating system, in memory.
break mirror	[Storage System] Remove a component from a mirror and make it an independent volume in the system, ending its synchronization with the other mirror components.
bridge	[Network], [Fibre Channel] [Network] A technology that enables traffic from a source device using one physical transport network technology to be transmitted to the destination device using an alternative physical transport network technology. In some cases a bridge is referred to as a physical transport gateway or storage router. [Network] A device that connects multiple LAN segments at the physical address layer. As opposed to a hub, which indiscriminately rebroadcasts everything from one segment to the other, a bridge only retransmits traffic from one segment to another when the traffic is intended for the destination segment. [Fibre Channel] A Fibre Channel technology that provides a transparent Fibre Channel Fabric extension between two Fibre Channel Switch E_Ports through the use of two B_Ports tunneling through some alternative technology, resulting in an Inter-Switch Link.
broadcast	A single transmission of a message to all receivers connected to a transport network. Broadcast can be contrasted with unicast (sending a single message to a single receiver) and multicast (sending a single message to select subset of receivers).
buffer	[Computer System] A solid state memory device or programming construct, used to hold data momentarily as it moves along an I/O path or between software components.
buffer-to-buffer credit	Value used to determine how many frames can be sent to a recipient when buffer-to-buffer flow control is in use. See Credit.
buffer-to-buffer flow control	[Fibre Channel] Flow control between two connected ports. Flow control occurs between two connected Fibre Channel ports (e.g., an N_Port and its associated F_Port or two E_Ports). A port indicates the number of frames that can be sent to it (i.e., its buffer-to-buffer credit) before the sender is required to stop transmitting and wait for the receipt of additional credit.
business continuity	[Data Security] Capability of an organization to continue the delivery of products or services at acceptable predefined levels following a disruption [ISO 22300:2018]
bypass circuit	[Fibre Channel] A circuit that provides for removal of a device from a data path. A device may be removed from a data path (e.g., a Fibre Channel Arbitrated Loop) if valid signaling is lost or if a controller directs the removal of the device for any reason.
byte	[Computer System] An 8 bit unit of data. Byte and bit ordering and meaning vary depending on context. It is necessary to consult the standards that apply in a given context to determine ordering and meaning.
B_Port	[Fibre Channel] The bridge port within a bridge used to extend an Inter-Switch Link.