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I mainly write because I'm using the rrdtool holt-winters feature, but sadly it does not work as I would, starting I'll write for you the rrd file command line creation:

`/usr/bin/rrdtool create /home/spread/httphw/rrd/httpr.rrd --start $_[7]-60 --step 60 DS:200:GAUGE:120:U:U RRA:AVERAGE:0.5:1:1440 RRA:HWPREDICT:1440:0.1:0.0035:288  RRA:AVERAGE:0.5:6:700 RRA:AVERAGE:0.5:24:775 RRA:AVERAGE:0.5:288:797`;

After that I basically insert data and then I draw the graph like that:

`/usr/bin/rrdtool graph file.png --start $start --end $time --width 600 --height 200 --imgformat PNG DEF:doscents=$rrd:200:AVERAGE DEF:pred=$rrd:200:HWPREDICT DEF:dev=$rrd:200:DEVPREDICT DEF:fail=$rrd:200:FAILURES TICK:fail#ffffa0:1.0:"Failures Average" CDEF:scale200=doscents,8,* CDEF:upper=pred,dev,2,*,+ CDEF:lower=pred,dev,2,*,- CDEF:scaledupper=upper,8,* CDEF:scaledlower=lower,8,*  LINE1:scale200#0000ff:"Average" LINE1:scaledupper#ff0000:"Upper Bound Average" LINE1:scaledlower#ff0000:"Lower Bound Average"`;

Here's the image RRDTOOL IMAGE

The I get a graph like that, but as you can see there's yellow lines that indicates that there has been an error when that's not true, I mean, the activity line at that point is slightly out from the red area but it does not an error, I basically need to understand the values I gotta set up and based on what, I tried it out but I don't really understand the system really well.

Any sugestion from an rrdtool expert?

Many thanks in advance

arrrrgv
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2 Answers2

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The Holt-Winters FAILURES RRA is a slightly more complex than just 'outside the range HWPREDICT+-2*DEVPREDICT'. In fact, there are the additional threshold and window parameters, which (if not specified, as in your case) default to 7 and 9 respectively.

These cause a smoothing of the samples over window samples before comparison, and only trigger a FAILURE flag when there is a sequence of threshold consecutive errors.

As a result, you see a FAILURE trigger where you do, and not in the larger area to the left (which averages down within the range). This results in a better indicator of consistently our of range behaviour, rather than a slope slightly too early or a temporary spike.

If you want to avoid this, and have a FAILURE flag every time the data goes outside of the predicted bounds, then set the FAILURE parameters to 1 and 1. To do this, you would need to explicitly define the additional HW RRAs rather than having them defined implicitly as you do now.

On a separate note, is is bad practice to have a DS with a purely numerical name. It can cause confusion in the RPN calculations. Always have a DS name start with a lowercase letter.

Steve Shipway
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Being outside the expected range is an error, as far as Holt-Winters is concerned.

Vatine
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