RAIDZ Capacity Calculator

This works out what a ZFS pool actually holds, which is always less than the disks add up to and usually less than the parity ratio suggests. Pick a vdev type, the number of disks, the disk size, the sector size and the record size, and it returns the raw capacity, the parity-only figure, the figure after raidz padding, the reserve ZFS keeps back and the usable total in both decimal TB and binary TiB. The padding step follows the allocation rule in ZFS itself: parity is added per stripe row and the result is rounded up to a multiple of one more than the parity count, so a ten-wide RAID-Z2 stores about 76 per cent of raw rather than 80. Compression, dedup, snapshots and metadata are not counted, because how much they move the figure depends entirely on what you put in the pool.