<< Previous Section Getting Started: Cacti as an RRDTool Front-end [home] Next Section >>

Getting Started: Cacti as an RRDTool Front-end

Cacti is a true RRDTool front-end in that it tries to make use of RRDTool's core graph and data storage features. Since Cacti relies heavily on RRDTool, there are a few RRDTool specific terms and concepts that it is useful to know before diving into Cacti.

RRAs and RRDs

The basic unit of storage in RRDTool is the round robin archive (RRA). Round robin archives control what kinds of data to keep, how often to store that data, and how long to keep that data. Of course a unit of storage is not very useful without data, and this is where the data source comes in. A round robin database (RRD) contains both round robin archives and data sources and is how you will store all of your data in RRDTool. In Cacti, the "Data Sources" menu option directly corresponds to these RRD files and is how to you define data for graphs in Cacti.

CDEFs and GPRINTs

When making graphs with Cacti, there are two terms that you are destined to run into. The first is a CDEF, which is simply a way to mathematically alter the data on the graph. Cacti lets you define CDEFs just as you can in RRDTool, and are explained very well in Tobi's RPN or CDEF tutorials. Secondly, you are apt to run into the term GPRINT, which is simply a way to alter the text-output of your graph values. The number format defined for GPRINTs is the same as printf() if you are used to c, and is described in the RRDTool graph manual.