Redundant Array of Inexpensive disks (RAID)::

RAID is a fault tolerant method of storing data, meaning that a failure can occur and the system will still function. The various RAID categories are:
0 - Disk striping - Data is written across multiple drives in parallel. Different parts of the data is written at the same time to more than one drive. If there are two drives, half the data is written to one drive, while the rest of the data is written to the other drive. All partitions on striped drives must be the same size. No fault tolerance is provided with RAID-0.
1 - Disk mirroring - All the data is written to two drives so each drive has a complete of all stored data. If one drive fails, the other can be used to get a copy of the data. To be more fault tolerant, more than one controller card may be used to control the mirrored hard drives. This is called disk duplexing and will allow the system to keep functioning if one controller card fails.
2 - Disk striping with error correction codes (ECC).
3 - Disk striping with ECC parity information stored on a separate drive.
4 - Disk striping with blocks with parity information stored on a separate drive.
5 - Disk striping with blocks with parity information stored using multiple drives. Uses five disks with one fifth of each one to store parity information.
Sector Sparing

Sector sparing will detect when data is going to be read from or written to a bad sector on the hard drive and will move the data to a good sector. The bad sector is marked as not available so it is not used again.
Windows NT support

Supports RAID-0,1, and 5 along with sector sparing.

Terms:
DAT - Digital Audio Tape
Sector Sparing - A method of fault tolerance that automatically identifies and marks bad sectors as not available. It is also called hot-fixing.
SLED - Single Large Inexpensive disk - The concept that a large disk costs less per amount of storage than several smaller ones. Somehow this concept is used as a means of fault tolerance.