Any tips on selecting a drive and port for the parity drive?
Yes, see Improving unRAID Performance#Move Parity Drive Off PCI Bus. Also, when writing to the array the overall speed is often limited by the rotational speed of the disks involved. This is because when writing to a disk the existing contents of each sector being written must first be read, then parity calculations made, and finally the same sector written. To write a sector that was previously read, the platter on the disk must revolve at least once before the disk head can get to the sector to write it. For this reason, if possible, use a disk with a higher rotational speed for the parity disk, as it is involved in every “write” to the array. All that said, there are many of unRAID servers with older IDE drives (or “green” drives) that spin at slower speeds, so don’t worry if your parity drive spins at 5400 RPM. It will be slightly slower to write to, because it spins slower, but will still be perfectly usable.
