Definitions for "RAID 4"
As in RAID 0, RAID 4 distributes data among the hard disks. However, RAID 4 uses one hard disk to save parity data. This makes it possible to restore the data from crashed hard disks from the saved parity data.
similar to Level 3 but provides faster performance because it uses blocks for striping.
RAID 4 is commonly called guarding. It uses data striping, like RAID 0, but adds a single, dedicated parity drive. The parity data stored on this drive can be used to recover data lost from a single failed drive. RAID 4 configurations write data slowly because parity data has to be generated and written to the parity drive, and the generation of the parity data frequently requires reading data from multiple physical drives. See also guarding and striping.