The first thing that comes to mind is that something has a file open,
which was later deleted. Such a deleted file will not show up in du
because it can't be listed, but the blocks the file is using will still
be reported by df. If you have the lsof command installed (apt-get
install lsof) you can try something like lsof | grep -i del | grep
/megastorage
to identify deleted files and the process which has it open.
Mike Stone
Thanks for your reply.
lsof | grep -i del | grep /megastorage
shows nothing