Parity computations are used in RAID drive arrays for fault tolerance by calculating the data in two drives and storing the results on a third. The parity is computed by XOR'ing a bit from drive 1 ...

For more than three drives, I'd suggest moving up to RAID 5 or 6. With a drive fail tolerance of one and two, respectively, they're ideal for those with lots of data to store on NAS. Parity data ...