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Raid glossary

Terms from the RAID world explained

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 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 reside on the 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 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.

Microprocessor - A processor on the RAID card which performs all RAID management functions. 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 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 - Redundant Array of Independent /Inexpensive disks.

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.