[rrd-users] Re: xff of RRA ?

[Alex van den Bogaerdt]

Cody Lo wrote:

> I have RRDTool monitoring for my equipments well, I'm really appreciate
> with it. But one thing I don't understand is the the xff of the RRA
> while creating it.
> 
> xff The xfiles factor defines what part of a consolidation interval may
> be made up from *UNKNOWN* data while the consolidated value is still
> regarded as known.

The consolidation interval is the amount of time that each slot in
the RRA covers.  For instance, if "--step" == 300 and the RRA uses
6 "steps" to build one row, the amount of time is 1800 seconds (30
minutes).

xff determines the part of this half hour that may be unknown.

> In some of the examples, the value of xff is 0.5, which is likely to
> mean 5 minutes.

No, it is not.  It is a number between 0 and 1 ( 0 <= xff < 1 )

> But how will it behaves when I have this value set to 0.
> 1 ? or some other values ? 3 ?

Look at it as a percentage.  Multiply the number by 100 and you
will understand it better I think.

0.5  -->  50%  -->  half of the intervals used (3 steps * 300
seconds in the example) may be unknown to build one, known,
interval (6 steps * 300 seconds).

0.0  -->  0%  -->  every  PDP (look this up on the faq site if
needed) must be known in order to build a known CDP (dito).

0.999 --> almost 100% --> a known CDP is built even if there's
only one known PDP out of many PDPs.

HTH
-- 
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