UFS 200GB of my partition space disappear

Hello, I have FreeBSD 9.1-RELEASE running. After partitioned, I got 1.8TB left for usr. After a time running, I saw that I used up to 1.6TB and my partition is 100% full.

So, question is where is my 200GB space?
df -h
Filesystem    Size    Used   Avail Capacity  Mounted on
/dev/da0p2    991M    145M    766M    16%    /
devfs         1.0k    1.0k      0B   100%    /dev
/dev/da0p4    495M     28k    455M     0%    /tmp
/dev/da0p5    9.7G    302M    8.6G     3%    /var
/dev/da0p6    1.8T    1.6T   -110M   100%    /usr
FreeBSD 9.1 has been End-of-Life since December 2014 and is not supported any more. Please upgrade to a supported version as soon as possible.

Check where your data may have filled: du -s /usr/* | sort -n. The largest sized directory will be at the bottom, drill down using du(1) until you find the directory that has filled up the partition.

Question is where is my 200GB space?

From tunefs(8):
     -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-

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

             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.

8% of disk space will be reserved and is only accessible for root.