zfs: the exponential file system from hell

[Attila Nagy]

Hi,

Did anyone try to fill a zpool with multiple zfs in it and graph the 
space accounted by df and zpool list?
If not, here it is:
https://picasaweb.google.com/104147045962330059540/FreeBSDZfsVsDf#5928271443977601554

The zpool in question:
         NAME        STATE     READ WRITE CKSUM
         mnt         ONLINE       0     0     0
           raidz2-0  ONLINE       0     0     0
             da1     ONLINE       0     0     0
             da2     ONLINE       0     0     0
             da3     ONLINE       0     0     0
             da4     ONLINE       0     0     0
           raidz2-1  ONLINE       0     0     0
             da5     ONLINE       0     0     0
             da6     ONLINE       0     0     0
             da7     ONLINE       0     0     0
             da8     ONLINE       0     0     0
           raidz2-2  ONLINE       0     0     0
             da9     ONLINE       0     0     0
             da10    ONLINE       0     0     0
             da11    ONLINE       0     0     0
             da13    ONLINE       0     0     0

And the zfs-es on it:
NAME     USED  AVAIL  REFER  MOUNTPOINT
mnt     23.3G      0  53.8K  /mnt
mnt/p1  3.89G      0  3.89G  /mnt/p1
mnt/p2  3.89G      0  3.89G  /mnt/p2
mnt/p3  3.89G      0  3.89G  /mnt/p3
mnt/p4  3.89G      0  3.89G  /mnt/p4
mnt/p5  3.89G      0  3.89G  /mnt/p5
mnt/p6  3.89G      0  3.89G  /mnt/p6

I have evenly filled the six zfs in 1/100th percents of the full space 
available, and graphed the results of zpool list's capacity and df's 
capacity.
The x scale is the real space usage in percents.

It's quite annoying when df says the file systems are 20% full, while in 
reality, they are at 60%.

Any chance that it will be solved?