ZFS and df weirdness

[Dan Naumov]

Hello list.

I have a single 2tb disk used on a 7.2-release/amd64 system with a
small part of it given to UFS and most of the disk given to a single
"simple" zfs pool with several filesystems without redundancy. I've
noticed a really weird thing regarding what "df" reports regarding the
"total space" of one of my filesystems:

atom# zpool list
NAME                    SIZE    USED   AVAIL    CAP  HEALTH     ALTROOT
tank                   1.80T    294G   1.51T    15%  ONLINE     -

atom# zfs list
NAME              USED  AVAIL  REFER  MOUNTPOINT
tank              294G  1.48T    18K  none
tank/DATA         292G  1.48T   292G  /DATA
tank/home         216K  1.48T    21K  /home
tank/home/jago    132K  1.48T   132K  /home/jago
tank/home/karni    62K  1.48T    62K  /home/karni
tank/usr         1.33G  1.48T    18K  none
tank/usr/local    455M  1.48T   455M  /usr/local
tank/usr/obj       18K  1.48T    18K  /usr/obj
tank/usr/ports    412M  1.48T   412M  /usr/ports
tank/usr/src      495M  1.48T   495M  /usr/src
tank/var          320K  1.48T    18K  none
tank/var/log      302K  1.48T   302K  /var/log

atom# df
Filesystem      1K-blocks       Used      Avail Capacity  Mounted on
/dev/ad12s1a      16244334   1032310   13912478     7%    /
devfs                    1         1          0   100%    /dev
linprocfs                4         4          0   100%    /usr/compat/linux/proc
tank/DATA       1897835904 306397056 1591438848    16%    /DATA
tank/home       1591438848         0 1591438848     0%    /home
tank/home/jago  1591438976       128 1591438848     0%    /home/jago
tank/home/karni 1591438848         0 1591438848     0%    /home/karni
tank/usr/local  1591905024    466176 1591438848     0%    /usr/local
tank/usr/obj    1591438848         0 1591438848     0%    /usr/obj
tank/usr/ports  1591860864    422016 1591438848     0%    /usr/ports
tank/usr/src    1591945600    506752 1591438848     0%    /usr/src
tank/var/log    1591439104       256 1591438848     0%    /var/log

atom# df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/ad12s1a        15G    1.0G     13G     7%    /
devfs              1.0K    1.0K      0B   100%    /dev
linprocfs          4.0K    4.0K      0B   100%    /usr/compat/linux/proc
tank/DATA          1.8T    292G    1.5T    16%    /DATA
tank/home          1.5T      0B    1.5T     0%    /home
tank/home/jago     1.5T    128K    1.5T     0%    /home/jago
tank/home/karni    1.5T      0B    1.5T     0%    /home/karni
tank/usr/local     1.5T    455M    1.5T     0%    /usr/local
tank/usr/obj       1.5T      0B    1.5T     0%    /usr/obj
tank/usr/ports     1.5T    412M    1.5T     0%    /usr/ports
tank/usr/src       1.5T    495M    1.5T     0%    /usr/src
tank/var/log       1.5T    256K    1.5T     0%    /var/log

Considering that every single filesystem is part of the exact same
pool, with no custom options whatsoever used during filesystem
creation (except for mountpoints), why is the size of tank/DATA 1.8T
while the others are 1.5T?


- Sincerely,
Dan Naumov