[rrd-users] Re: multiple RRAs in a single RRD
Alex van den Bogaerdt
alex at ergens.op.het.net
Wed Nov 20 23:59:10 MET 2002
On Wed, Nov 20, 2002 at 09:12:57PM +0000, Jim Breton wrote:
> What is the advantage of having multiple archives (with different sample
> intervals) if you are only graphing one of these?
You're not, as Tobi explained.
> For example, if I am graphing network i/o on a system and taking samples
> every 5 minutes, why would I also want to create another RRA which takes
> samples once per hour?
An RRA doesn't take samples. An RRA stores normalized and consolidated
data. It is ready to graph data.
> I realize that would make a useful graph as well,
> but I don't see how to "get it out" of the RRA when you graph it, since
> it's under the same Data Source; so as far as I can tell the only way to
> determine hourly results based on the above RRD would be to extrapolate
> your 5-minute samples. But I'm sure I must be missing something!
If you're going to generate an image where each pixel shows one hour
of data, you don't want to to the math on 12 5-minute samples for
each of your 400 pixels. It is much faster when you already have
the data in a 1-hour resolution at hand. You don't *need* it, it
is just nice to have.
a) retrieve 12 samples, add them, divide by 12, display
b) retrieve 1 sample, display
Another good reason is that you may want to choose not to store 2 years
worth of data in a 5-minute resolution. Unless of course you want to
actually display the data from way back in high resolution.
a) 365+366 days * 288 samples per day = 210528 samples
b) 2.5 days * 288 samples and 365+366 days * 1 sample = 1451 samples
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