I was replying yesterday when you posted again to say that one of the solutions had worked.
Re the plugin method, there is another plugin which sees any changes to the clearsync.d/ folder and restarts clearsync which will read the new plugin. The problem I have with this method is that in the past I've had to make a few attempts to get the file right, so what I posted may not work and I didn't have time to test. I suspect it was the other method which worked after rebooting. I was just putting up a little script with an infinite loop which deleted core.* every second when you posted that you'd had success. In reflection it would have been easier than the plugin as it only needed 4 lines of code.
Longer term, I suggest you install logwatch. It runs nightly and e-mails you a report of various activities on your system and includes the output of "df -h".