I'm planning to start pooling all my old disks and turning on duplication, moving on from SnapRAID so I can more easily just add disks of any size to the pool. Anyway, I'm banking on basically halving the capacity of all my disks to determine usable capacity, but I vaguely understand that it's not that simple. FWIW, I'm planning to pool 3, 3, 3, and 5TB drives.
I'd also like to be able to see the "usable" capacity of the pool instead of the raw capacity when using duplication. i.e., if I have 14TB of raw disk and deduplication is set for the whole pool, can it show me 7TB of usable space?