Some useful steps when dealing with a disk space problem:
1) What has been modified in the last day
find /opt -mtime -1
2) Find the size of a folder in human readable disk sizes:
du -h /tmp
don't forget the very useful
% du -sh *
to list the sizes of all the files / folders in pwd
and
% du -s * | sort -n
to sort folders by size, doesn't work with human readable but is very handy for finding that home directory which suddenly has 200 gigs of log files in it.