Hi I have the same question. The answer is clear, that is if you know what you are talking about. I''m not al that good in IT stuf if it comes to programming ;)
So please, for me some more information (in a simple way) were to put /var/db/collectd/rrd/localhost/
I have one graphic that I want to get rid of, because it does not exist in the system anymore.
I have freenas 9.1.1
Thanks!