I think his problems is (like we all have i think) is that that disk gets full if you don't keep an eye on it.
We have 100gb disk and around 15gb free. But alot of time is goes down to 5gb. Restarting the apache service(or restartings helps alot). acces.log file get very big its automatically removed bij restarting the service or de server. (For us it was 11gb Last month :/) But i think last reboot was 5-6 months before this.We keep our revisions around 25.
We don't have big problems but we came from 40gb disk 2 years ago.. :P