Disappearing available space with ZFS...what am I missing?

[Aaron]

I've created a ZFS pool with zpool create tank raidz ada0 ada1 ada2
ada3, and then I add some additional mountpoints (I think they're
called) using zfs create tank/storage, etc. In zpool list, I see the
pool with 3.62T available. With df -h, I see 2.4T available for tank,
and tank/storage. When I first created tank, it had the 3.62T
available as I expected. What am I missing? I do have compression set
to gzip-9 on tank which gets inherited like I want, don't know if that
would affect anything.

--Aaron