df reports negative (minus) value FreeBSD

It was really surprise for me, Today is my first day working with FreeBSD after 11 years linux administration 🙂

ms3# df -h
Filesystem       Size    Used   Avail Capacity  Mounted on
/dev/mfid0s1a     29G    5.9G     21G    22%    /
devfs            1.0K    1.0K      0B   100%    /dev
/dev/mfid0s1f    213G    9.9G    186G     5%    /hast
/dev/mfid0s1d    2.9G    2.7M    2.7G     0%    /tmp
/dev/mfid0s1g     97G     77G     12G    86%    /usr/local
/dev/mfid0s1e     29G    1.1G     26G     4%    /var
/dev/mfid1s1d    451G    421G   -6.8G   102%    /opt1
linprocfs        4.0K    4.0K      0B   100%    /usr/compat/linux/proc
ms3#

It`s o.k. it means, that I just using reserved space. (available for root, n/a for users.)

man tunefs

     -m minfree
             Specify the percentage of space held back from normal users; the
             minimum free space threshold.  The default value used is 8%.
             Note that lowering the threshold can adversely affect perfor-
             mance:

             o   Settings of 5% and less force space optimization to always be
                 used which will greatly increase the overhead for file
                 writes.

             o   The file system's ability to avoid fragmentation will be
                 reduced when the total free space, including the reserve,
                 drops below 15%.  As free space approaches zero, throughput
                 can degrade by up to a factor of three over the performance
                 obtained at a 10% threshold.

             If the value is raised above the current usage level, users will
             be unable to allocate files until enough files have been deleted
             to get under the higher threshold

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