In Linux, it is possible to delete a file that has been opened by multiple processes. If you stop one of the process and delete the file without stopping the other process, the system will still show the disk space as being used.
I recently had this happen, I had a MySQL database that was using 29GB of storage space. I stopped the database, deleted the files and recreated the database. Once complete, I noticed that I didn't reclaim any of the used space.
Continue reading Whats eating my disk space? (Invisible files)