Glossary of RAID Terminology

Array
Two or more hard disk drives grouped together to appear as a single device to the host computer.

Bootable Array Support
The ability to make the system boot from a RAID array instead of from a stand alone (single) disk.

Cache
A temporary, fast storage area that holds data from a slower storage device for quick access. Cache storage is normally transparent to the accessing device.

Co-processor
A processor that resides on an array that relieves the host CPU from executing processor-intensive operations such as RAID 5 parity calculations and secondary RAID 1 writes.

Duplexing
Mirroring across two RAID cards.

Dynamic Array Expansion
See “Online Capacity Expansion”

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

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

Microprocessor
A processor on the RAID card which performs all RAID management functions (for example, the Intel i960). Microprocessors offer higher performance compared to co-processors.

Mirroring (RAID 1)
Provides data protection by duplicating all data from a primary drive on a secondary drive.

NOS
Network Operating System (i.e., NetWare, Windows NT server)

Online Capacity Expansion (O.C.E.)
A process for adding storage capacity to an existing RAID array without having to take the server offline. Also known as Dynamic Array Expansion.

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

RAID Levels
Numbered 0 through 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 0
See “Striping”

RAID 0/1
Combines RAID 0 (data striping) and RAID 1 (disk mirroring).

RAID 1
See “Mirroring”

RAID 5
Combines data striping (for enhanced performance) with distributed parity (for data protection) to provide a recovery path in case of failure.

RAID Management Software
Software that makes installation, configuration, and management of RAID arrays easy. Often includes features such as pager notification and remote management.

SCSI
Stands for Small Computer System Interface. SCSI is the technology that allows you to connect various devices to your PC. This connection is made using a SCSI card that fits inside your computer.

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

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