This technique allows reconstruction of all data that was present on any single drive that has failed. Benefits Much better storage efficiency compared to mirroring. Better reliability than RAID 1. Read performance is excellent. More reliable than RAID 0 Better storage efficiency than RAID 1 Lower cost than RAID 2 More performance than RAID 3 Drawbacks Since there is a single disk that contains error correction data, whenever any other disk is updated, the error correction disk must also be updated.
Write performance is limited to the throughput of a single disk.
RAID 4 does not appear to be commercially viable and is rarely used. The parity data is distributed across the drives in such a way that a data group and its parity information are always written to different devices. This technique allows reconstruction of all data that was present on any single drive that has failed. Benefits Read performance can be quite good. Reliability will be high.