[rrd-users] Invalid alpha parameter for forecasting

Steve Shipway s.shipway at auckland.ac.nz
Wed Jan 15 23:01:53 CET 2014

> I'm trying to create a RRD with RRA for prediction, but each time I receive
> "Invalid alpha: must be between 0 and 1" error, no matter what value I set.
> This happens even when I try the examples from the documentation, for
> example this one, where alpha value is obviously between 0 and 1
> rrdtool create monitor.rrd --step 300        \
>    DS:ifOutOctets:COUNTER:1800:0:4294967295   \
>    RRA:AVERAGE:0.5:1:2016                     \
>    RRA:HWPREDICT:1440:0.1:0.0035:288

I haven't tested this, but I believe the reason is that for HW forecasting, you must have a SET of HW RRAs.  

Thus, just HWPREDICT on its own will not work.  It needs to also have a SEASONAL, DEVSEASONAL, FAILURES, and DEVPREDICT to go with it.  I had thought that rrdtool create would automatically create the additional RRAs but possibly that was a feature added later.

The above command line works for me (RRDtool 1.4.trunk) and you do not state which version of rrdtool you are using - possibly yours predates the autocreation or is simply an outdated buggy version.

I would try (1) explicitly creating all the RRAs in the HW set, or (2) upgrading RRDtool to the 1.4.latest version.


Steve Shipway
ITS Unix Services Design Lead
University of Auckland, New Zealand
Floor 1, 58 Symonds Street, Auckland
Phone: +64 (0)9 3737599 ext 86487
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Email: s.shipway at auckland.ac.nz
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