[rrd-users] rrdupdate

Alex van den Bogaerdt alex at ergens.op.het.net
Tue Dec 25 13:13:58 CET 2007

On Tue, Dec 25, 2007 at 02:31:07PM +0400, rihad wrote:

> > If you REALLY need to fiddle with your historical data, then you will 
> > need to export the data, alter the values in the XML file, then 
> > import that into a new database.
> > 
> Wow, absolutely amazing! So these are the hidden costs of MRTG -> 
> rrdtool migration? :-) Thanks for the solution, though, I shall try that.

You get extra protection for your historic data and are complaining?

Anyway, don't forget you need to edit all RRAs covering the timespan,
not just one.  MRTG-style RRAs have:

Each row 5 minutes, AVERAGE, and a MAX
Each row 30 minutes, AVERAGE, and a MAX
Each row 120 minutes, AVERAGE, and a MAX
Each row 1440 minutes, AVERAGE, and a MAX

You will need to modify each AVERAGE, and you will at least have to look
if each MAX should be changed.

An example:
You are going to remove a rate "55" from the database.  You find it
in the 5-minute RRA and remove it. You notice the surrounding rates are
all set to "1".

If you would only alter that "55" into "NaN", then you didn't do your
job properly. The 30-minute AVERAGE RRA still contains a rate "10",
which should be corrected to "1". The 30-minute MAX RRA still contains
rate "55", which should be corrected into "1". And so on.

Make sure you understand consolidation before you edit your RRD. You need
to do these computations yourself, and store the results.

Alex van den Bogaerdt

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