Tonight I noticed that the website was very slow so I checked if there was enough free space available. And the /var partition was 100% full again, while I had just cleaned it up yesterday.

So I did a quick sanity check and quickly found that I had left MySQL logging on "verbose", with this result:

A 2.5 GB log file on a 3.0 GB partition... So there is clearly no need for a new hard disk yet.