Glossary of Storage Terms

AIT

"Advanced Intelligent Tape", a high-speed, high-capacity magnetic tape data storage format developed and controlled by Sony. Uses the helical scan method of reading and writing to tapes.

Areal Density

Refers to the amount of data that can be stored in a given amount of hard disk platter. Since disk platters surfaces are two-dimensional, areal density is a measure of the number of bits that can be stored in a unit of area. It is usually expressed in bits per square inch (BPSI). Sometimes it is referred to as bit density. Higher areas of density under the right circumstances can improve the disks transfer rate.

Auxiliary Storage/ External Storage/ Secondary Storage

Data not directly accessible to the CPU, requiring the use of computers input/output channels.

Bit

A binary digit, taking the value of either a zero or a one. It is the smallest amount of information in a binary digital system.

Byte

A unit of measurement of information storage, most often consisting of eight bits. Eight bits of information can represent 256 different states. In many computer architectures it is a unit of memory addressing.

DAFS

"Direct Access File System" is a network file system similar to NFS and CIFS that allows applications to transfer data while bypassing operating system control, network protocol and buffering operations that can bottleneck throughput thus degrading performance.

DAS

“Direct Attached Storage” a digital storage system directly attached to a server or workstation without a storage network in between. Mainly used to differentiate non-networked storage from SAN and NAS.

DLT

"Digital Linear Tape" technology is a magnetic tape data storage technology. DLT uses linear serpentine recording with multiple tracks on half-inch wide tape.

Exabyte

A unit of storage equal to 1 quintillion bytes or 1 billion Gigabytes.

FC

"Fibre Channel" is a gigabit-speed network technology primarily used for connecting mass storage devices and tape libraries to computer systems.

GBIC

An acronym for "Gigabit Interface Converter". A GBIC is a standard for transceivers commonly used with Gigabit Ethernet and Fibre Channel. By offering a standard, hot swappable electrical interface, one gigabit ethernet port can support a wide range of physical media from copper to long-wave single-mode optical fiber at lengths of hundreds of kilometers.

Gigabyte

A unit of information or computer storage equal to 1,024 Megabytes. Abbreviated GB, not to be confused with Gb, which is used for gigabits.

HBA

"Host Bus Adapter", connects a host system (the computer) to other network and storage devices.

Hot Plug/Hot Swap

The ability to install or remove components of a computer, while it is operating.

iSCSI

Small Computer System Interface protocol over an IP network. Unlike other network storage protocols, such as Fibre Channel which is the foundation of most SANs, it requires only the simple and ubiquitous ethernet interface, or any other TCP/IPcapable network to operate. This enables low-cost centralization of storage without the expense normally associated with Fibre Channel storage area networks.

JBOD

"Just a Bunch OF Disks", used to refer to hard disks that aren't configured according to RAID.

Kilobyte

A unit of information or computer storage equal to 1,024 Bytes. Abbreviated K, Kb, Kbyte, and kB.

LTO

"Linear Tape-Open", is a magnetic tape data storage technology developed as an open alternative to the proprietary Digital Linear Tape (DLT). Developed jointly by IBM, HP, and Seagate.

Megabyte

A unit of information or computer storage abbreviated as M or MB, equal to 1,024 x 1,024 = 1,048,576 bytes. Not to be confused with Mb which is used for Megabit.

Mirror Site

A Mirror Site is an exact copy of another Internet site or set of files on a computer system. Mirror sites are most commonly used to provide multiple sources of the same information and are of particular value as a way of providing reliable access to large downloads. A mirror site will also will ensure better availability and can increase performance. Mirroring is a type of file synchronization.

NAS

"Network Attached Storage", is a file-level data storage connected to a computer network providing data access to heterogeneous network clients. NAS uses file-based protocols providing both storage and file system storage.

Nibble

A 4 Bit aggregation - or half an octet.

Petabyte

A unit information or computer storage equal to 1,024 Terabytes, or just over a million Gigabytes. Abbreviated as PB.

RAID

"Redundant Array of Independent Drives", originally known as Redundant Array of Inexpensive Drives, RAID is an umbrella term for data storage schemes that divide and/or replicate data among multiple hard drives. RAID can be designed to provide increased reliability and/or increased I/O performance.

SAN

"Storage Area Network" is architecture that attaches remote computer storage devices such as disk arrays, tape libraries and optical jukeboxes to servers in such a way that, to the operating system the devices appear as locally attached devices.

SCSI

An acronym for "Small Computer System Interface". A set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with iSCSI and serial SCSI. Pronounced "skuzzy".

SDLT/SuperDLT

"Super Digital Linear Tape" technology, a variant with higher capacity can store from 110 GB to 300GB on a single cartridge and can transfer data at speeds of up to 10 megabytes per second. SDLT adds an optical servo system that reads servo patterns on the back of the tape in order to keep the data tracks on the front of the tape correctly aligned with the read/write heads.

NIA

"Storage Networking Industry Association" is an association of producers and consumers of storage networking products, whose goal is to further storage networking technology and applications. SNIA was incorporated in December 1997 whose members are dedicated to "ensuring that storage networks become complete and trusted solutions across the IT community."

Storage Consolidation

Terabyte

A unit of information or computer storage equal to 1,024 Gigabytes. Abbreviated as T or TB, not to be confused with Tb, which is a terabit.

Storage Virtualization

Physical storage resources are aggregated into storage pools, from which the logical storage is created. Multiple independent storage devices which may be scattered over a network, appear to the user as a single, location-independent, monolithic storage device which can be managed centrally.

WORM

"Write Once Read Many" times is a type of computer storage media that can be written to once, but read from multiple times. There are two types of WORM storage media: those that physically can be written only once, such as CD-R and DVD-R and media that enables WORM capability by using electronic keys or other measures to prevent rewriting.