Redundancy and parity
RAID level 1, 4, and 5 arrays generate parity
information, which is stored separately from the data it
If a disk in the array fails, the parity information and the partial data on the remaining disks are used to reconstruct the data on the failed disk. If the failed disk is the disk used for parity storage (in RAID level 4), the data from all the good disks is used to regenerate the lost parity information while the subsystem continues normal operations.