One morning, I started wondering how RAID 5 parity works to rebuild a disk array. It seemed “magical” to me, that you can get redundancy and still use most of your disk capacity. So I searched for it… and turned up not very much info, and one other person’s unanswered question. A few articles explained it, but in a little more detail about performance, and less detail about the actual parity function. This article attempts to fill the gap.