This looks like OS issue, not VCS.
If memory serves me right, df reserves about 10% in space calculation. That is why df can report disk usage of more than 100%.
Found this:
http://docs.oracle.com/cd/E23824_01/html/821-1451/spmonitor-6.html
Use the df command to show the amount of free disk space on each mounted disk. The usable disk space that is reported by df reflects only 90 percent of full capacity, as the reporting statistics allows for 10 percent above the total available space. This head room normally stays empty for better performance.
The percentage of disk space actually reported by the df command is used space divided by usable space.