[rrd-users] rrd step > 1h ==> strange start times of RRAs

[Thorsten Volkmer-Wolf]

Hi,

a may be strange thing i don't understand. Executing the following command (starting date string represents Feb 04, 08:00 local time)


>rrdtool create test.rrd \
>    -b  1075878000 --step 3600 \
>    DS:var1:GAUGE:86400:U:U RRA:MAX:0.5:1:5 \
>    DS:var2:GAUGE:86400:U:U RRA:MAX:0.5:1:5

and then

>rrdtool dump mail.rrd

gives the following output for the RRAs:


------------------snip----------------------------
....
<!-- 2004-02-04 04:00:00 CET / 1075863600 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 05:00:00 CET / 1075867200 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 06:00:00 CET / 1075870800 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 07:00:00 CET / 1075874400 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 08:00:00 CET / 1075878000 --> <row><v> NaN </v><v> NaN </v></row>
</database>
------------------snap----------------------------


Well, thats what i would expect. Starting date is 2004-02-04 at 08:00 CET, and the entrys 'step down' with a gap of 3600 seconds, which is indeed one hour. Fine.

Now, lets change the command line and set the step to two hours:

>rrdtool create test.rrd \
>    -b  1075878000 --step 7200 \
>    DS:var1:GAUGE:86400:U:U RRA:MAX:0.5:1:5 \
>    DS:var2:GAUGE:86400:U:U RRA:MAX:0.5:1:5


and now

>rrdtool dump mail.rrd

gives me this:

------------------snip----------------------------
<!-- 2004-02-03 23:00:00 CET / 1075845600 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 01:00:00 CET / 1075852800 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 03:00:00 CET / 1075860000 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 05:00:00 CET / 1075867200 --> <row><v> NaN </v><v> NaN </v></row>
<!-- 2004-02-04 07:00:00 CET / 1075874400 --> <row><v> NaN </v><v> NaN </v></row>
</database>
------------------snap----------------------------

. Hmm....the step is ok (two hours as wanted), but what has happened to the time slot for the latest value? It has changed to 2004-02-04 07:00:00, allthough i didn't change the start time of the rrd. 

What's the thing i haven't understood so far?




rrdtool 1.0.45-1 on debian linux 2.4.19-xfs



Thank you very much in advance,

	Thorsten

++
Dipl.-Ing.
Thorsten Volkmer-Wolf
IT-Support & Services

AEROTEC Engineering GmbH
Hein-Saß-Weg 38
21129 Hamburg / Germany

fon +49 (0)40/742 198-241
fax +49 (0)40/742 198-111

<http://www.aerotec.de>

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