Munin – Load old/historic data from a database to prepopulate the graphs

RRDtool, which munin uses behind the scenes, can be used perfectly well for this purpose; although it's usually used for frequently updated data, it works just as well if you tell it that it'll only be getting data points once a day or once a week. However, munin isn't flexible enough to take advantage of this feature of RRDtool (as per http://munin.projects.linpro.no/ticket/5), so you're either stuck with doing it by hand (seriously, rrdtool is easy to use) or finding a data collection and graphing that isn't so dodgy.

I think DERIVED values must be integer values, so either round them or use GAUGE.