rrd – snmp
rrd is a database that works like a 5 gallon bucket with a hose coming out the bottom: You put stuff in until it overflows, and it keeps a steady 5 gallons of “information” in it at all times and just rotates through. It’s just a normal file on your server but it’s specially dedicated to this rotating process. It’s typically used for graphing some small history of a given dataset and then dumping the old stuff you no longer care about. When you combine it with snmp, it can monitor stuff on your network and feed it to a graphing thing so you can keep a historical graph of trends on your network.
Here are a few links: