RAID kaj je to?

RAID Advisory Board
Pa še na kratko:

Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.

There are number of different RAID levels. The three most common are 0, 3, and 5:

Level 0: Provides data striping (spreading out blocks of each file across multiple disks) but no redundancy. This improves performance but does not deliver fault tolerance.
Level 1: Provides disk mirroring.
Level 3: Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance.
Level 5: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance.