Its reserved space. ext3 default 5% reserve is 135GB for your filesystem. You need at least ~162GB or so of free space to see something besides 100%. To reduce reserved space use the tune2fs command.
Reserved space reduces fragmentation and allows root to login if the filesystem becomes full. Since this is a data drive you can reduce the amount of reserved space to zero if necessary.
Last edited by michaelk; 04-05-2010 at 08:59 AM.