* RAID 0 (striped disks) distributes data across several disks in a way that gives improved speed at any given instant. If one disk fails, however, all of the data on the array will be lost, as there is neither parity nor mirroring. In this regard, RAID 0 is somewhat of a misnomer, in that RAID is 0 is non-redundant. A RAID 0 array requires a minimum of two drives.
* RAID 1 mirrors the contents of the disks, making a form of 1:1 ratio realtime backup. The contents of each disk in the array are identical to that of every other disk in the array. A RAID 1 array requires a minimum of two drives.
* RAID 4 (striped disks with dedicated parity) combines three or more disks in a way that protects data against loss of any one disk. The storage capacity of the array is reduced by one disk. A RAID 3 array requires a minimum of three drives; Two to hold striped data, and a third drive to hold parity data.
* RAID 5 (striped disks with distributed parity) combines three or more disks in a way that protects data against the loss of any one disk. The storage capacity of the array is a function of the number of drives minus the space needed to store parity.
* RAID 6 (striped disks with dual parity) combines four or more disks in a way that protects data against loss of any two disks.
* RAID 10 (or 1+0) is a mirrored data set (RAID 1) which is then striped (RAID 0), hence the "1+0" name. A RAID 10 array requires a minimum of two drives, but is more commonly implemented with 4 drives to take advantage of speed benefits.
* RAID 01 (or 0+1) is a striped data set (RAID 0) which is then mirrored. (RAID 1). A RAID 01 array requires a minimum of four drives; Two to hold the striped data, plus another two required to mirror the pair.
http://en.wikipedia.org/wiki/RAID