RAID 4 consists of block-level striping with a dedicated parity disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk and checked on Reads.
RAID 4 requires at least 3 drives to implement.
Characteristics & Advantages
Very high Read data transfer rate
High random read rate
The ratio of Parity disks to data disks is low, which means higher efficiency
Controller design is fairly complex
Worst write transaction rate
Data rebuild is difficult and inefficient during disk failure