Showing wrong disk space

[deami]

This may be a newbie question, but I've just updated my server's Debian 3 build to Sarge and had to recreate one graph for the large partition on my server (all the other graphs went on working fine). This partition is about 220GB, but the graph is only showing it as 900MB total, with a used percentace far lower than it really is. The partition itself is just fine. I can read from and write to it just like normal and the mount is showing its correct size from my Windows PC.

Is there something I'm missing here?