I'm building a RAIDZ2 ZFS system, using Ubuntu 13.10 as a base system, and zfsonlinux's packages, having 6 disks dedicated to the pool data and a couple of SSD partitions to do ZIL log and L2ARC cache. My HDDs are all 2.0 TiB (in fact: slightly less than 2.0 TiB) drives.
Yet, once the pool was created, zpool list unexpectedly reports a pool having 10.9 TiB size, 1.93 MiB allocated, and 10.9 TiB free. How is it getting nearly 11 TiB free in a RAIDZ2 having a total of 12.0 TiB of disks? I was expecting to have a mere 8.0 TiB of free space (4.0 TiB being allocated to parity).
Oh, this is apparently a very similar question to ZRAID1 pool size bigger than expected, but about RAIDZ2 instead of RAIDZ… I'll post this anyway, in case anyone cares about RAIDZ2 for their searches.
Best Answer
It turns out that each drive is 1.82TiB. That, times 6 = 10.9TiB. I suppose zpool reports the total physical space available for filesystem labour (ie: data + parity) as opposed to just the space available for user data without the parity factored in.
In fact, the "duplicate question" has a perfectly good answer already, quoted here (added dashes for clarity):
PS. Maybe we should have a "raidz2" tag.