Why is there a mismatch between df and du outputs?

One of the things that GFS has to address is a file that has been unlinked, but not deallocated, when the system dies. It does this by adding a marker into the journal saying there is a floating inode when a file is unlinked.

When the inode is finally deallocated, the marker is removed from the journal. After a crash, systems finds those markers in the "looking for log elements" stage o...