RAID system designers and administrators of storage have to make several other decisions as well.
For example, how many disks should be in a given RAID set?
How many bits should be protected by each parity bit? If more disks are in an array, data-transfer rates are higher, but the system is more expensive.
If more bits are protected by a parity bit, the space overhead due to parity bits is lower, but the chance that a second disk will fail before the first failed disk is repaired is greater, and that will result in data loss.