Parity codes provide error detection and correction. RAID-2 is fast for large file transfers, but less efficient for small file transfers, because all drives in the array are accessed for every request. Drive thoughput, for any manufacturer's implementation of a RAID is also determined by the application, block size of the data transfers, and operating system. Data is transferred in parallel to data and parity drives. The parity drive stores a complementary copy of the parity information When a data drive fails, the remaining data drives and the parity drive together can recreate the missing information.
Access time is determined by the number of drives in the array.
Because it takes less time to only send part of a data byte to each drive, the more drives in an array, the faster the throughput. Ideally an array's performance approaches the limits of its interface's capability which is far greater than the real world performance of a single drive. RAID-4 has multiple data drives supported by a single redundant parity checking drive. While only a single write can take place at any time, because the parity drive must be updated, multiple concurrent reads from two or more drives are supported. Therefore, many more read requests can be handled per second than writes.