So what's the alternative? How do you prevent a DoS attack against the system (ie,filling up the hard drive) .. ???
You can use quotas at the OS level. For FreeBSD: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/quotas.html. Similar things exist for those "other" :-) unix-y operating systems.
In the worst case you can have a cronjob running that calculates the size and performs adequate actions for the situation. Luckily it takes time to fill up a disk and this "solution" could actually work for small to medium sized installations.
-Bob
