[rrd-users] Do RRD files grow?

Simon Hobson linux at thehobsons.co.uk
Thu Jun 19 17:59:27 CEST 2014

Kevin Stewart <kstewart at vaonet.com> wrote:

> Once an RRD is created, as points are added, will the file grow over 
> time? Or does the file stay the same size (given that is is not tuned)?

As Pablo says, they are pre-allocated and stay the same size - that size is known because you define all the DSs (data series), consolidations, and retention periods (ie number of consolidated data points to keep) when you create the file. Internally it is as the name says, a round robin. Each consolidated data set is defined by a single list of values - plus a pointer to the current "start/end". As new data comes in, it simply over-writes the oldest data and the pointer moved on - when the pointer gets to the end, it wraps around to the beginning. So nothing is "added" or "removed" - only updated in-place.

However I'm not sure what you mean by "not tuned" - because RRD files are actually quite highly tuned for a specific purpose, that of efficiently storing/extracting/graphing predefined sets of data as above.

As a bit of trivia, RRD Tools came out of the MRTG project - a set of tools to collect, consolidate, and graph interface traffic rates for routers (hence Multi Router Traffic Grapher).

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