I had some large files (over 200GB in total size) that I no longer
needed.  So I removed them.  They no longer show up in the directory. 
However, df, still shows the space as being used.  I understand that if
processes are still using the files they will not be removed until the
processes either release them, or are shut down (or killed).  I have
tried using 'lsof -a -L1 MOUNTPOINT' to list the open, but deleted
files.  It returns no files at all.

These files are on a removable drive.  I can unmount the partition and
disconnect the drive, then reconnect the drive and remount the
partition, but the space still shows as being used. If the files are
still open, shouldn't 'umount' give an error?

I would rather not have to shut down the system.  Is there some other
way to determine what is keeping these files open, or otherwise
preventing the space from being reclaimed?

Marc