[rrd-users] Re: Overlapping RRAs

[Serge Maandag]

> > > rrdtool create test.rrd
> > > 	DS:myvalues:COUNTER:600:U:U
> > > 	RRA:AVERAGE:0.5:1:27360		## 95 days
> > > *	RRA:AVERAGE:0.5:6:336		## 7 days
> > > *	RRA:AVERAGE:0.5:24:372		## 31 days
> > > 	RRA:AVERAGE:0.5:288:365		## 365 days
> > > *	RRA:MIN:0.5:1:27360		## 95 days
> > > 	RRA:MIN:0.5:6:336		## 7 days
> > > 	RRA:MIN:0.5:24:372		## 31 days
> > > 	RRA:MIN:0.5:288:365		## 365 days
> > > *	RRA:MAX:0.5:1:27360		## 95 days
> > > 	RRA:MAX:0.5:6:336		## 7 days
> > > 	RRA:MAX:0.5:24:372		## 31 days
> > > 	RRA:MAX:0.5:288:365		## 365 days

> Yes, I agree and disagree with you, but maybe I'm missing something. I
> think the the last two entries for 95 days are redundant, because it's
> only 1 sample being taken meaning the MIN. MAX and AVERAGE will be the
> same. Or am I looking at it in the wrong way ?

In these RRA's:

> > > 	RRA:AVERAGE:0.5:1:27360		## 95 days
> > > *	RRA:MIN:0.5:1:27360		## 95 days
> > > *	RRA:MAX:0.5:1:27360		## 95 days

MIN, MAX and AVERAGE are always the same, except perhaps, when you
update 
more then once within a step interval.

All the other RRA's have multiple pdp's per cdp, so they consolidate
multiple
values. Take these RRA's:

> > > 	RRA:AVERAGE:0.5:6:336	## 7 days
> > > 	RRA:MIN:0.5:6:336		## 7 days
> > > 	RRA:MAX:0.5:6:336		## 7 days

If you updated your RRA just once every step value and you updated the
rrd db with 
the values 1,2,3,4,5,6 the result will be: MIN=1 AVERAGE=3.5 MAX=6. So
here MIN
and MAX are not quite redundant.

So why define a RRA with one pdp per cdp? Well you may want to update
more than once 
per step interval and I think you need them to be able to graph them in
a high resolution.

Serge.

p.s I did not study the source code, so some of my assumptions also may
be erroneous. 

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