The directory /data was being used to nfs mount a remote file system. However, there were some LOCAL directories under /data also. Unmounting /data and removing the local subdirectories fixed the problem.
du -x was only seeing the remote files and certainly not reporting any file space consumption; it was unable to see the local subdirectories. On the contrary, df doesn't care about what is mounted and reports the real partition utilization. I will always trust df over du :) -- Pedro I. Sanchez
