ZFS space allocation

Hi,

I just upgraded a 13.3-RELEASE system to 14.1-RELEASE, which has
two ZFS pools, z for ZFS-on-root and storage for asorted stuff. While
a 'pkg upgrade' fails, I discovered something strange with the free
disk space.

'zpool list' reports
NAME      SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
storage  9.50G  7.90G  1.60G        -         -    75%    83%  1.00x    ONLINE  -
z          17G  16.5G   532M        -         -    88%    96%  1.00x    ONLINE  -

but 'df -hi' reports

Filesystem             Size    Used   Avail Capacity iused ifree %iused  Mounted on
z/ROOT/default         3.7G    3.7G      0B   100%    170k     0  100%   /
devfs                  1.0K      0B    1.0K     0%       0     0     -   /dev
tmpfs                  256M    4.0K    256M     0%       1  918k    0%   /tmp
fdescfs                1.0K      0B    1.0K     0%       4  114k    0%   /dev/fd
procfs                 8.0K      0B    8.0K     0%       0     0     -   /proc
z/home                 180M    180M      0B   100%     445     0  100%   /home
z/tmp                  128K    128K      0B   100%      13     0  100%   /tmp
z                       96K     96K      0B   100%       7     0  100%   /z
storage                1.3G     96K    1.3G     0%       9  2.7M    0%   /storage
z/usr/ports             96K     96K      0B   100%       7     0  100%   /usr/ports
z/var/log              4.8M    4.8M      0B   100%      99     0  100%   /var/log
z/var/audit            2.0M    2.0M      0B   100%      27     0  100%   /var/audit
z/var/crash             96K     96K      0B   100%       8     0  100%   /var/crash
z/var/tmp              104K    104K      0B   100%      14     0  100%   /var/tmp
z/var/mail             140K    140K      0B   100%      18     0  100%   /var/mail


In general I don't have any clue where the 16.5G are allocated.

Any hints how to get the space back? I have deleted all snapshots, but the available space
is still 0B.

--Gordon