RAID - Glossary

Array
Two or more disks grouped together to appear as a single disk to the host system. See also disk array.

Background Initialization
The initialization process of a disk array takes place in the background, allowing immediate availability of disk array within seconds instead of several hours.

Bridge RAID Controller
A device which is typically used to control external RAID subsystems as compared to Internal PCI-based RAID subsystems. It bridges to multiple devices. A bridge RAID controller is also referred as an External RAID Controller.

Controller
A controller is often used with peripheral devices such as network controller, keyboard controller, RAID controller, SCSI controller.

Degraded Mode
A RAID mode used when a component drive has failed.

Disk Array
A disk array which contains multiple disk drives. Disk arrays, also known as RAID, allow disk drives to be used together to improve fault tolerance, performance, or both. Disk arrays are commonly used on servers.

Duplexing
Mirroring across two RAID cards.

External RAID Controller
External RAID controllers are often referred to as a Bridge RAID Controller. See Bridge RAID Controller.

Fault Tolerance
The ability of a system to continue to perform its functions even when one or more hard disk drives have failed.

Global Spare
An extra, physical disk drive placed in an array and used as a Hot Spare. A global spare automatically takes the place of a failed drive.

Hot Spare
A spare hard drive which will automatically be used to replace the failed member of the redundant disk array.

Hot Swap
The ability to remove a failed member of a redundant disk array and replace it with a good drive without bringing down the server or interrupting transactions that involve other devices.

Internal RAID Controller
A controller circuit board that resides inside a computer or server. An internal RAID controller resides on a bus, such as the PCI bus.

Mirrored Hard Drive
Two hard drives the computer sees as one unit. Information is stored simultaneously on each drive. If one hard disk drive fails, the other contains all of the cached data and the system can continue operating.

Mirroring
The complete duplication of data on one disk drive to another disk drive, this duplication occurs simultaneously with each write operation.

Parity
A form of data protection used by RAID level 5 to recreate the data of a failed drive in a disk array.

RAID
Redundant Array of Independent Disks, a collection of two or more disks working together in an array. RAID has different level. The three most commonly used are 0, 1, and 5.

Raid Levels
Numbered 0 to 5, RAID levels refer to different array architectures that offer various advantages in terms of data availability, cost and performance.RAID levels 0, 1, 0/1, and 5 are the most popular.

RAID Advisory Board (RAB)
An association of companies whose primary intention is to standardize RAID storage systems.

RAID Migration
A feature in RAID subsystems that allows for changing a RAID level to another level without powering down the system.

Recovery
The process of reconstructing data from a failed disk using data from other drives. More on www.optimumrecovery.com

Striping (RAID 0)
Spreads data evenly over multiple drives to enhance performance. Because there is no redundancy scheme it does not provide data protection.