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===== Tom's RRd Notes =====

This is an informal collection of notes to help me understand an RRD database.





==== Creation ====
The RRD database is created with the following syntax:

   rrdtool create target.rrd \
         --start 1023654125 \
         --step 300 \
         DS:mem:GAUGE:600:0:671744 \
         RRA:AVERAGE:0.5:12:24 \
         RRA:AVERAGE:0.5:288:31

In this example, **target.rrd** is the name of the database.\\
The **start time** in epoch seconds is given by --start 1023654125\\
The **step** is the time frequency in seconds. --step 300\\
**DS** is a keyword meaning DataSource followed by the variable name, in this case "mem".\\
**GAUGE** is the type of data which can be COUNTER, DERIVE, ABSOLUTE, GAUGE.Use GAUGE to store the data itself.\\
Next is the **heartbeat**, set to 600 here. If the database doesn't get an update every 300 seconds, in the next 300 second update it will store an UNKNOWN for the missed reading.\\
The next two parms are minimum and maximum values if known. Any values outside these two parms are set to unknown. The min and max shown here are 0 and 671744.\\