RAID 4

RAID 4 features data re-creation through a combination of RAID 0 striping and the use of a dedicated parity disk.
Data is divided into unit blocks and kept on dedicated data disk drives while parity data is kept on a single dedicated parity disk.

When updating it is necessary to pre-read both the existing and parity data and write updated parity data when the update is complete. This process is referred to as having a "write penalty".

It is usually impossible to implement this process in business environments as the dedicated parity disk becomes a bottleneck during traffic surges and performance suffers.