thx for input ... but ...

df only gives me the whole lot (what i allready have, because df in cron is setting the alarm). ANY find takes quite some while. find . -print for instance takes 59 minutes. So i think i have to strip down a global search into "sneaking" into specific directories to keep the response within a reasonable timerange (30 to 60 minutes). a pitty, that "du" always goes all way down it's tree in directory.