This bash-script gives You an easy way to generate a new RRD - but be aware of overwriting an existing one!
After downloading the script, You have to make it executable by running
chmod +x create_rrd.sh
To change parameter of the RRD, just open the script in Your favorite editor and change all settings You want. For example You can add another datasource (sensor) by cloning the last line beginning with DS: and changing the name from vol to the name of the other datasource (e.g. smoke).