Hello!
I am aware, that generally your parity drives need to be at least as large as your largest data disk.
Here is the thing:
I ordered a 16 TB WD Elements from Amazon, but the nice guys shipped me a 18TB. I am running dual parity with 2x 16TB Exos drives. I just tried to add this to my array, expecting it to just add it (with only 16 TB useable). I am used for this to work with Synology NAS systems, where you can only use as much space as the parity allows, when you then upgrade parity disks the additional space gets allocated. Sadly, unraid doesn't let me do this and expects a parity swap procedure instead.
Before I put my 18TB to the side until I can afford DECENT 18TB parity drives (don't fancy those "internal use" WDs as parity compared to the great performing EXOS drives). Is there really no other way?