Site.getDiskUsage ()
function returns the used disk space for this site in Kilobyte

Sourcecode in Site/objectFunctions.js:
1:   function getDiskUsage() {
2:      if (this.diskusage == null) {
3:         this.diskusage = 0;
4:         for (var i=0; i<this.files.count(); i++)
5:            this.diskusage += this.files.get(i).filesize;
6:         for (var i=0; i<this.images.count(); i++) {
7:            if (this.images.get(i).filesize == null)
8:               this.images.get(i).filesize = this.images.get(i).getFile().getLength();
9:            this.diskusage += this.images.get(i).filesize;
10:        }
11:     }
12:     return Math.round(this.diskusage / 1024);
13:  }