5. Database support for MRTG
 

The classic version of MRTG does not store any historical SNMP data for future inquiries and graphs generation. It only collects the SNMP info and rebuilds the variation graphs on the fly. There are 4 types of graphs: daily, weekly, monthly and yearly for which MRTG stores the graph images only. 

As the average calculation period increases (weekly, monthly, yearly) the SNMP values are calculated with an average value for that extended period. If you want to know what the network utilization was at a specific date/time, with a 5min average calculation, then it will not be available. 

The database support that was given to MRTG by RRDTOOL comes with extended capabilities, which makes MRTG a more complex network analysis tool. 

The backend database stores the SNMP values for as long as you configure it through the database size parameters. You will be able to generate detailed variation graphs for past times, with a very precise average calculation (lowest is 5min). 

The database support is named RRDTOOL and it is a Round-Robin database. An individual database is kept for each individual monitored entity. 

The database has a fixed size, which can be defined and modified by an administrator. The values are stored in the database in a sequential manner, as when the database gets full, the new values are written over the oldest values (FIFO algorithm – first in, first out). 

The database can be configured to store a specific number of records, which permits to size it for a specific period of time based on the number of SNMP read actions. 

The database support can be configured to run in parallel with the classic collect-and-graph MRTG functionality.