[rrd-users] Re: A beginners question

[Alex van den Bogaerdt]

paulw at oninit.com wrote:

> Is there a limit to number of RRAs that can be stored in a single
> rrd file?  Are there performance fall offs once you get above a
> particuler number of RRAs in a single rrd?

If there is a limit I wouldn't know of it.  Of course, the file
size will grow and you may hit an OS limitation !

RRAs are used to consolidate the data a collection time.  This saves
time and resources at graph time.  If you create a lot of graphs and
carefully design your RRAs, you may even use lesser resources in the
end.  OTOH, for setups that need virtually no graphing/fetching except
once in a while and automated, it may be a waste to implement more
than one RRA.

For a RRA to be really effective, you need to create a graph that is
querying for data in exactly the resolution this RRA contains.

Example: if you create a graph with a size of 400 pixels, and the
time span of this graph is 100 hours, each pixel represents exactly
15 minutes.  In this case it is useful (but not necessary) to have
a RRA that contains consolidated data in that resolution.  If there
is only a RRA with data in 300-second resolution, the data will be
consolidated at graph time.  The end result is the same, it is the
moment when consolidating occurs.

Of course, if you're never going to create this graph, it isn't
useful at all to have this RRA and it is just a waste of resources.

HTH,
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