0: Speed without fault-tolerance.
The simplest and fastest of the RAID levels, data is split into equal-sized blocks, and each block is written to a separate disk. Because I/O load is spread over several disks, throughput is greatly improved.
Mirroring and parity are not implemented, therfore, the overhead associated with these operations do not exist. However it is not fault-tolerant at all. If one of the disks fail, the whole array is useless. Thus RAID 0 is not considered a true RAID.