I have setup a mrtg setup with rrdtool. Now I'm planning to get incoming outgoing usage data from these RRD files and failing to find a correct way to do it.
Can anyone show we how to get those usage data from rrd files?
Then I can maintain a db to keep those usage data and calculate the cost etc.?
you can use rrdtool graph ... PRINT:xxx or rather rrdtool xport ... to get data out of the rrd file. If you want to get to the actual data, use rrdtool fetch.
you can find tons of additional info on http://rrdtool.org