RAID 2 implements bit-level striping with hamming code ECC, it's the only RAID level that does not use one or more of the typical RAID techniques of mirroring, striping and/or parity. RAID 2 is realized splitting data at bit level and spreding it over a number of data discs and a number of redundancy discs. The redundant bits are calculated through Hamming codes. Every time some data is going to be written on the array these codes are calculated and written alongside the data to dedicated ECC disc. During reading ECC codes are read as well to assure no error have occurred since data writing.

Controller Requirements:supported by specialized controllers
Hard Disk Requirements:RAID 2 implementation typically requires 14 discs, 10 data discs and 4 ECC discs
Array Capacity:size of the smallest drive
Storage Efficiency:if drives are the same size 50%
Fault tolerance:very good, improved by using duplexing variant
Availability:very good, most RAID controllers support hot sparing and automatic rebuilding
Degradation and rebuilding:read performance a little degraded, write performance improved
Random read performance:good, worse than many other RAID levels but better then single drive
Random write performance:good, better than many other RIAD levels but worse than single drive
Sequential read performance:more or less the same as single drive
Sequential write performance:good, better than many other RAID levels