RAID 4
RAID 4 definition
RAID 4 stands for “redundant array of independent disks, level 4.” It’s a storage configuration that divides data into blocks across multiple disks with a separate, dedicated disk solely for storing parity information. This setup ensures data integrity and fault tolerance.
See also: fault tolerance, data redundancy, data center storage, hot spare
RAID 4 structure
In RAID 4, data is divided into blocks, and each block is written to a separate disk drive. This means that if you have data blocks A, B, C, and D and four disks, block A will be written to Disk 1, block B to Disk 2, block C to Disk 3, and block D to Disk 4. This is called data striping.
Unlike the even distribution of data blocks, RAID 4 uses a dedicated disk for storing parity information. If you had four data disks, there would be a fifth disk just for parity. This parity data provides a way to reconstruct data from the remaining disks if one disk fails.
RAID 4 functions
- Fault tolerance. The dedicated parity disk allows the RAID array to continue functioning even if one of the data disks fails. If a disk does fail, the data on that disk can be reconstructed using the remaining data disks and the parity disk.
- Performance. Due to the striping, read operations can be quite fast because multiple disks can be read concurrently. However, write operations can be slower compared to other RAID configurations. Every time data is written to a disk, the parity information must be updated, which involves reading the old data, reading the old parity, computing the new parity, and then writing the new data and the new parity. This process can cause a bottleneck since all write operations require access to the dedicated parity disk.