RAID 2
RAID 2 employs the use of Error Correction Codes (ECC), these are also referred to as Hamming Codes (named after Richard Hamming of Bell Labs, who invented them). They provide the ability to search for and correct errors in data.
Data is divided into bit or byte units, and kept on multiple dedicated data drives.
In practice however, RAID 2 is little used as it is inferior to other RAID levels in terms of both cost and performance.
