SAN technology and arrays Definitions

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  • A

    AHCI (Advanced Host Controller Interface)

    Advanced Host Controller Interface, or AHCI, is a technical standard for an interface that enables software to communicate with Serial ATA (SATA) devices.

  • areal density

    Areal density measures the amount of data that can be stored on a given amount of physical space on a disk drive.

  • ASPI (Advanced SCSI Programming Interface)

    ASPI (Advanced SCSI Programming Interface) specifies how an application program can communicate with a SCSI (Small Computer System Interface) device through a common SCSI device driver.

  • ATA over Ethernet (AoE)

    ATA over Ethernet (AoE) is an open source network protocol designed to connect storage devices and servers in a storage area network (SAN). ATA (Advanced Technology Attachment) is a standard interface for communication between storage devices; it is known in the computer industry as Integrated Drive Electronics, or IDE. In AoE, the ATA commands are transported directly via Ethernet. That makes AoE an inexpensive alternative to Fibre Channel SANs, which require costly dedicated networks.

  • B

    bad block

    A bad block is an area of storage media that is no longer reliable for storing and retrieving data because it has been physically damaged or corrupted.

  • BEDO DRAM (Burst Extended Data Output DRAM)

    BEDO DRAM (Burst Extended Data Output DRAM) is a type of dynamic random access memory (DRAM) that can send data back to the computer from one read operation at the same time it is reading in the address of the next data to be sent.

  • bit rot

    Bit rot is the slow deterioration in the performance and integrity of data stored on storage media. It is also known by the names bit decay, data rot, data decay and silent corruption.

  • block storage

    Block storage is an approach to data storage in which each storage volume acts as an individual hard drive that is configured by the storage administrator. In the block storage model, data is saved to the storage media in fixed-sized chunks called blocks.

  • Blue Book

    The Blue Book is the informal name for the standard specification document for stamped multisession (also known as the enhanced CD or E-CD) disk format, developed in 1995 from a supplement to Philips and Sony's 1988 Orange Book.

  • buffer credits or buffer-to-buffer credits (BBCs)

    Buffer credits, also called buffer-to-buffer credits (BBCs), allow data communication in a Fibre Channelstorage area network (SAN) where there are long spans of fiber opticcable.

  • C

    converged network adapter (CNA)

    A converged network adapter (CNA) is a single network interface card (NIC) that contains both a Fibre Channel (FC) host bus adapter (HBA) and a TCP/IP Ethernet NIC.

  • D

    DASD (direct access storage device)

    Direct access storage device (DASD, pronounced DAZ-dee), is a general term for magnetic disk storage devices. The term has historically been used in the mainframe and minicomputer (mid-range computer) environments.

  • data retention

    Data retention, also called records retention, is the continued storage of an organization's data for compliance or business reasons. 

  • defragmenter

    A defragmenter is a software utility that rearranges the fragments or discontiguous parts of each file stored on a computer hard disk so that the small, empty storage spaces adjacent to fragments can be used, effectively creating new storage space and possibly making file access faster.

  • Dell EqualLogic

    Dell EqualLogic storage-area network arrays provide varying capacities of hard disk drives and solid-state drives using iSCSI and SATA controllers.

  • disk array

    A disk array, also called a storage array, is a data storage system used for block-based storage, file-based storage or object storage.

  • disk cache

    A disk cache is a mechanism for improving the time it takes to read from or write to a hard disk.

  • disk duplexing

    Disk duplexing is a variation of disk mirroring in which each of multiple storage disks has its own SCSI controller.

  • disk striping

    Disk striping divides data into blocks and spreads the blocks across hard disks or solid-state drives to accelerate read and write access.

  • disk-to-disk-to-tape (D2D2T)

    Disk-to-disk-to-tape (D2D2T) is an approach to computer storage backup and archiving in which data is initially copied to backup storage on a disk and then later on copied again to tape.

  • diskette (floppy disk)

    A diskette is a random access, removable data storage medium that can be used with personal computers.

  • Double-Density Compact Disk (DDCD)

    Double-Density Compact Disk (DDCD) is a CD format that increases the storage capacity of the disk through means such as increasing the number of tracks and pits (scores on the disk that are used to encode the data).

  • double-parity RAID

    Double-parity RAID (redundant array of independent disks), also called diagonal-parity RAID, Advanced Data Guarding (RAID_ADG), or RAID-6, is a method of protecting against multiple storage drive failures by creating two sets of parity data on an array of hard disks.

  • E

    enterprise storage

    Enterprise storage is a centralized repository for business information that provides common data management, protection and data sharing functions through connections to computer systems.

  • Express Bay

    Express Bay is an externally accessible storage slot that is designed to accept a high-performance PCI Express (PCIe) solid-state drive (SSD),

  • F

    FCoE (Fibre Channel over Ethernet)

    FCoE (Fibre Channel over Ethernet) is a storage protocol that enable Fibre Channel communications to run directly over Ethernet. FCoE makes it possible to converges storage and IP protocol traffic onto a single cable transport and interface.

  • Fibre Channel

    Fibre Channel is a high-speed networking technology primarily used for transmitting data among data centers, computer servers, switches and storage at data rates of up to 128 Gbps.

  • Fibre Channel adapter

    A Fibre Channel (FC) adapter is a hardware component that provides connectivity from a server to a storage area network (SAN).

  • Fibre Channel Arbitrated Loop (FC-AL)

    A Fibre Channel Arbitrated Loop (FC-AL) is a high-speed Fibre Channel (FC) topology that can connect up to 126 ports on one controller using a one-way loop or hub design.

  • Fibre Channel director (FC director)

    A Fibre Channel (FC) director is a modular, chassis-based, high port-count switch that connects servers, switches and storage in a dedicated FC storage area network (SAN).

  • Fibre Channel Industry Association (FCIA)

    The Fibre Channel Industry Association (FCIA) is an international organization whose goal is to help its members promote Fibre Channel (FC) technology.

  • Fibre Channel over IP (FCIP or FC/IP)

    Fibre Channel over IP (FCIP or FC/IP, also known as Fibre Channel tunneling or storage tunneling) is an Internet Protocol (IP)-based storage networking technology developed by the Internet Engineering Task Force (IETF).

  • Fibre Channel port names

    Fibre Channel port names

  • Fibre Channel switch (FC switch)

    A Fibre Channel switch is a networking device that is compatible with the Fibre Channel (FC) protocol and designed for use in a dedicated storage area network (SAN).

  • FICON (Fiber Connectivity)

    FICON (for Fiber Connectivity) is a high-speed input/output (I/O) interface for mainframe computer connections to storage devices.

  • flash memory card

    Flash storage memory cards use nonvolatile semiconductor memory to store pictures, audio and video data on portable and remote devices.

  • G

    giant magnetoresistive effect

    GMR is the newest generation of hard disk drive storage.

  • gigabyte

    A gigabyte -- pronounced with two hard Gs -- is a unit of data storage capacity that is roughly equivalent to 1 billion bytes.

  • H

    hard disk

    A hard disk is part of a unit -- often called a disk drive, hard drive or hard disk drive -- that stores and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces.

  • hard disk drive (HDD)

    A computer hard disk drive (HDD) is a non-volatile memory hardware device that controls the positioning, reading and writing of the hard disk, which furnishes data storage.

  • hard drive shredder

    A hard drive shredder is a mechanical device that physically destroys old hard drives in such a way that the data they contain cannot be recovered.

  • hard zoning

    Hard zoning is used to allocate resources and control access in a storage-area network (SAN).

  • hardware RAID (hardware redundant array of independent disk)

    Hardware RAID is a form of RAID where processing is done externally.

  • HDD form factor (hard disk drive form factor)

    HDD form factor is the size or geometry of a hard disk drive, determining the device’s compatibility with the drive bays in a storage array or enclosure, server, portable computer or other computing device.

  • holographic disk drive

    A holographic disk drive is a holographic storage device that uses a laser to store data to optical media in three dimensions, maximizing storage capacity by using the media's depth... (Continued)

  • host bus adapter (HBA)

    A host bus adapter (HBA) provides physical connectivity and input/output between a server and a network and/or storage device.

  • hot plug

    Hot plug is the addition of a component to a running computer system without significant interruption to the operation of the system.

  • hot spare

    A hot spare, also called a hot standby, is a backup component that can be placed into service immediately when a primary component fails. 

  • HVD (holographic versatile disc)

    Holographic versatile disc (HVD) is a medium of holographic storage that looks like a DVD but is capable of storing far more data... (Continued)

  • hybrid hard drive (HHD)

    A hybrid hard drive (HHD), sometimes known as a solid-state hybrid drive (SSHD), is a mass storage device that combines a conventional hard disk drive and a NAND flash module.

  • Hyper-V Virtual Fibre Channel

    Virtual Fibre Channel is a feature in Microsoft Hyper-V 3.0 that lets virtual machines (VMs) connect directly to Fibre Channel (FC)-based storage by using a standard World Wide Name (WWN) associated with a VM.

  • I

    IDE (Integrated Drive Electronics)

    Integrated Drive Electronics (IDE) refers to the integration of the controller and drive.

  • iFCP (Internet Fibre Channel Protocol)

    iFCP (Internet Fibre Channel Protocol) is an emerging standard for extending Fibre Channel storage networks across the Internet.

  • InfiniBand

    InfiniBand is an architecture and specification for data flow between processors and I/O devices. The technology is most often used in high-performance computing (HPC) environments... (Continued)

  • intelligent switch

    An intelligent switch is a high-level storage area network (SAN) routing switch that provides features such as storage virtualization, quality of service (QoS), remote mirroring, data sharing, protocol conversion, and advanced security.

  • Internet Small Computer System Interface (iSCSI) adapter

    An iSCSI adapter is a network interface card that enables the transmission of data between host computers and iSCSI-based storage arrays and typically handles the TCP/IP processing.

  • IP SAN (Internet Protocol storage area network)

    An IP SAN is a dedicated storage area network (SAN) that allows multiple servers to access pools of shared block storage devices using storage protocols that depend on the Internet Engineering Taskforce standard Internet Protocol suite.

  • IP storage

    IP storage is a general term for several approaches to using the Internet Protocol (IP) in a storage area network (SAN) usually over Gigabit Ethernet.

  • iSCSI (Internet Small Computer System Interface)

    ISCSI is a transport layer protocol that describes how Small Computer System Interface (SCSI) packets should be transported over a TCP/IP network.

  • iSCSI initiator

    An iSCSI initiator is software or hardware that enables a host computer to transmit data to an iSCSI-based storage array through a network adapter over a TCP-based IP network.

  • iSCSI switch (Internet Small Computer System Interface switch)

    An iSCSI switch is an appliance that processes and channels data between an iSCSI initiator and target on a storage device.

  • J

    Jaz drive

    A Jaz drive is a small, portable hard disk drive used primarily for backing up and archiving personal computer files.

  • JBOD (just a bunch of disks or just a bunch of drives)

    JBOD ("just a bunch of disks") refers to a computer's hard disks that haven't been configured according to the RAID system.

  • K

    Kryder's Law

    Kryder's Law describes the rate at which former Seagate CTO Mark Kryder predicted disk drive density would grow.

  • L

    logical unit number (LUN)

    A logical unit number (LUN) is a unique identifier for designating an individual or collection of physical or virtual storage devices that execute input/output (I/O) commands with a host computer, as defined by the Small System Computer Interface (SCSI) standard.

  • LUN management

    LUN management is the process of assigning, provisioning and overseeing logical unit numbers (LUNs) across a storage environment.

  • LUN masking

    LUN masking is a further constraint added to zoning, subdividing access to the port so that only LUNs authorized to access a specific server can access the corresponding port.

  • LUN zoning

    LUN zoning is a method of configuring SAN fabric to match logical unit numbers (LUNs) to the proper servers. As a rule, end devices such as hosts can only see and access storage within their zone. Limiting access in this way improves security and allows bandwidth allocation through assigning particular ports to a zone.

  • M

    magneto-optical drive (MO)

    The magneto-optical (MO) drive is a popular way to back up files on a personal computer.

  • magnetoresistive head technology

    Magnetoresistive (MR) head technology is used in disk drives to allow higher storage densities than the older inductive-head technology.

  • Memory Stick

    Developed by Sony, the Memory Stick is a digital data storage technology with up to 10 times the storage capacity of a 3.5 diskette.

  • multipathing (SAN multipathing)

    Multipathing, also called SAN multipathing or I/O multipathing, is the establishment of multiple physical routes between a server and the storage device that supports it. 

  • N

    N_Port ID virtualization (NPIV)

    N_Port ID virtualization (NPIV) is a technology that allows a single host bus adaptor (HBA) called an "N_Port" to register multiple World Wide Port Names (WWPNs) and N_Port identification numbers.

  • O

    oversubscription

    Oversubscription, in a SAN (storage area network) switching environment, is the practice of connecting multiple devices to the same switch port to optimize switch use... (Continued)

  • P

    parity

    Parity is a method of detecting errors in data transmissions between computers, while parity bit and parity checking are used in RAID technology to guard against data loss.

  • partition

    Partitioning a hard disk drive is the first step in preparing it for data storage. A disk partition is a carved out logical space used to manage operating systems and files.

  • PLEDM (phase-state low electron drive memory)

    PLEDM (phase-state low electron drive memory) is a new memory microchip technology that offers vastly greater capacity than memory devices commonly used in the past.

  • R

    race condition

    A race condition is an undesirable situation that occurs when a device or system attempts to perform two or more operations at the same time, but because of the nature of the device or system, the operations must be done in the proper sequence to be done correctly.

  • RAID (redundant array of independent disks)

    RAID (redundant array of independent disks) is a way of storing the same data in different places on multiple hard disks or solid-state drives to protect data in the case of a drive failure.

  • RAID 0 (disk striping)

    RAID 0 (disk striping) is the process of dividing a body of data into blocks and spreading the data blocks across multiple storage devices, such as hard disks or solid-state drives (SSDs), in a redundant array of independent disks (RAID) group.

  • RAID 10 (RAID 1+0)

    RAID 10, also known as RAID 1+0, is a RAID configuration that combines disk mirroring and disk striping to protect data.

  • RAID 2

    RAID 2 is a technique that stripes data at the bit level using a Hamming code to detect errors.

  • RAID 3 (redundant array of independent disks)

    RAID 3 is a RAID configuration that uses striping and parity, but it uses a parity disk to store the parity information generated by a RAID controller instead of striping it with the data.

  • RAID 4 (redundant array of independent disks)

    RAID 4 is a RAID configuration that uses a dedicated parity disk and block-level striping across multiple disks.

  • RAID 5

    RAID 5 is a redundant array of independent disks configuration that uses disk striping with parity.

  • RAID 50 (RAID 5+0)

    RAID 50, also known as RAID 5+0, combines distributed parity (RAID 5) with striping (RAID 0).

  • RAID 6 (redundant array of independent disks)

    RAID 6, also known as double-parity RAID, uses two parity stripes on each disk. It allows for two disk failures within the RAID set before any data is lost.

  • RAID 7 (redundant array of independent disks)

    RAID 7 is a trademarked RAID level owned by the now defunct Storage Computer Corp. It is a non-standard RAID level that requires proprietary hardware.

  • RAID controller

    A RAID controller is a hardware device or software program used to manage hard disk drives (HDDs) or solid-state drives (SSDs) in a computer or storage array so they work as a logical unit.

  • RAMAC

    (IBM had an earlier system called RAMAC. See RAMAC (original).

  • RAMAC (random access method of accounting and control)

    RAMAC (which stood for 'random access method of accounting and control') was the world's first computer disk storage system... (Continued)

  • redundant

    Redundancy can have several meanings, but commonly refers to spare hardware that is kept online or to duplicate data.

  • Robson

    Robson is a mass storage system similar to a hybrid hard drive (HHD)... (Continued)

  • S

    SAN file system

    A SAN file system (that is, a storage area network file system) is programming that enables the sharing of the same copies of files stored on common storage media among multiple servers that may have different operating systems.

  • SAN island

    A SAN island is a storage area network (SAN) that exists as a discrete, isolated entity within a larger SAN. The components of a SAN island are usually all located in the same building, or even within a single room.

  • SAN routing

    SAN (storage area network) routing is a technology used for interconnecting SAN islands (separately designated logical portions of a storage area network) within a larger network.

  • SAN switch (storage area network switch)

    A storage area network (SAN) switch is a device that connects servers and shared pools of storage devices and is dedicated to moving storage traffic.

  • SAN-in-a-box

    A SAN-in-a-box, also known as a SAN-in-a-can or a SAN kit, is a data storage device that includes all the basic SAN components are in a single package.

  • SATA controller

    A SATA controller handles how hard drives are connected to a computer's motherboard.

  • SATA Express (SATAe)

    SATA Express (SATAe or Serial ATA Express) is a bus interface to connect storage devices to a computer motherboard, supporting SATA and PCI Express protocols simultaneously.

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