[rrd-users] Strange activity after a DST change

Smith, Kyle A. (Security) kasmith at tgslc.org
Tue Mar 11 15:59:46 CET 2008

Howdy all,
	I am a relatively new to rrdtool, but have setup a few
re-occuring charts for system metrics for 2 systems.  The process
(gathering the metrics from the systems, sending them to the 'local'
system housing rrdtool, updating the rrd db's, and generating the
graphs) has been working for a few months now without a hitch.. until
this past weekend when the system 'corrected' its time for local
daylight-savings.  The really annoying problem is that of the two
systems metrics/charts, only one is failing to display data/charts now,
the other charts fine.  I am stumped as I built the rrd db's, all the
updating scripts, and all the graphs identically (minus the system

The way I built it may be less then optimal, but I was learning as I
built it, and this isn't a production/customer usage process. The
process does more then just chart the load of the system, but this is
the most basic of the RRD db's.

Both load rrdb's were built like:

> rrdtool create $rrdroot/$server.load.rrd \
        -s 5 \
        --start -900d \
        DS:dsload:GAUGE:5:0:U \
        RRA:AVERAGE:0.5:12:360 \
        RRA:AVERAGE:0.5:720:1000 \

I backfilled data of almost 2.5 years before I started the 'live' data

The 'update' script push the live data feed to the rrdb:
> rrdtool update rrd/server3.load.rrd 1205245559:0.33
> rrdtool update rrd/server3.load.rrd 1205245565:0.36
> rrdtool update rrd/server3.load.rrd 1205245570:0.33
> rrdtool update rrd/server3.load.rrd 1205245576:0.30

So the data is stored in the rrdb:
> rrdtool lastupdate server3.load.rrd

1205245576: 0.30

But when I do:
> rrdtool dump  server3.load.rrd  | more
	<!-- 2008-03-11 09:26:00 CDT / 1205245560 --> <row><v> NaN
	<!-- 2008-03-11 09:27:00 CDT / 1205245620 --> <row><v> NaN

The only way I even know it started at DST change is later in the dump
for the hourly RRA:
		<!-- 2008-03-08 23:00:00 CST / 1205038800 --> <row><v>
1.1626519337e-01 </v></row>
            <!-- 2008-03-09 00:00:00 CST / 1205042400 --> <row><v>
1.4726296296e-01 </v></row>
		<!-- 2008-03-09 01:00:00 CST / 1205046000 --> <row><v>
1.0902040816e-01 </v></row>
            <!-- 2008-03-09 03:00:00 CDT / 1205049600 --> <row><v> NaN
		<!-- 2008-03-09 04:00:00 CDT / 1205053200 --> <row><v>
NaN </v></row>
            <!-- 2008-03-09 05:00:00 CDT / 1205056800 --> <row><v> NaN

This is using rrdtool on CentOS 5, Linux 2.6.16:
RRDtool 1.2.23  Copyright 1997-2007 by Tobias Oetiker <tobi at oetiker.ch>
               Compiled Jun  7 2007 00:19:10

Suggestions? I hope I am missing something fairly basic..  This is most
frustrating since one system's data is fine, while they others data

Kyle A Smith


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