Parity contains none of your data. Parity is just an extra bit that allows a missing bit to be calculated from all the other bits. Parity by itself can rebuild nothing. All bits of all other disks must be reliably read to reliably rebuild a disk.   This is basically the way parity works everywhere. Unraid just has its own implementation that allows each data disk to be accessed independently and so allows different sized disks in the parity array.   https://docs.unraid.net/un