RAID levels 2 and 3 make use of a parallel access technique where all member disks participate in the execution of every I/O requests.
Data striping is used in RAID levels 2 and 3, but the size of strips are very small, often a small as a single byte or word.
With RAID 2, an error-correcting code is calculated across corresponding bits on each data disk, and the bits of the cods are stored in the corresponding bit positions on multiple parity disks.
RAID 2 requires fewer disks than RAID 1. The number of redundant disks is proportional to the log of the number of data disks. For error-correcting, it uses Hamming code.
On a single read, all disks are simultaneously accessed. The requested data and the associated error correcting code are delivered to the array controller. If there is a single bit error, the controller can recognize and correct the error instantly, so that read access time is not slowed down.
On a single write, all data disks and parity disks must be accessed for the write operation.