Parity
Parity generates a set of redundancy data from two or more parent data sets. The redundancy data can be used to reconstruct one of the parent data sets. Parity data does not fully duplicate the parent data sets. In RAID, this method is applied to entire drives or stripes across all disk drives in an array. The types of parity are:
Type
Dedicated Parity
Distributed
Parity
Description
The parity of the data on two or more disk drives is stored on an additional disk.
The parity data is distributed across all drives in the system.
If a single disk drive fails, it can be rebuilt from the parity and the data on the remaining drives.
RAID level 3 combines dedicated parity with disk striping. The parity disk in RAID 3 is the last logical drive in a RAID set.
RAID level 5 combines distributed parity with disk striping. Parity provides redundancy for one drive failure without duplicating the contents of entire disk drives, but parity generation can slow the write process. A dedicated parity scheme during normal read/write operations is shown below:
12ADAC Ultra2 S466 Hardware Guide