[rrd-users] Odd gaps in RRD data

[David Cannings]

I have an RRD that I created like this:

rrdtool create simba-temperature.rrd \
 DS:mbtemp:GAUGE:300:0:100 \
 DS:cputemp:GAUGE:300:0:100 \
 RRA:AVERAGE:0.5:1:288 \
 RRA:MAX:0.5:1:288 \
 RRA:AVERAGE:0.5:12:168 \
 RRA:MAX:0.5:12:168

Every 5 minutes, a cronjob updates it.  However, I have some strange gaps 
in my RRD graphs and inspecting using:

"rrdtool fetch /root/rrd/simba-temperature.rrd AVERAGE"

Shows the following:

1075302000: 2.6000000000e+01 2.3000000000e+01
1075302300: nan nan
1075302600: 2.6000000000e+01 2.3000000000e+01
1075302900: 2.6000000000e+01 2.3398666667e+01
1075303200: nan nan
1075303500: 2.6000000000e+01 2.2400000000e+01
1075303800: 2.6000000000e+01 2.2001333333e+01
1075304100: 2.6000000000e+01 2.2996666667e+01
1075304400: 2.6000000000e+01 2.2402000000e+01

I'm positive the RRD has been updated every five minutes.  For one of the 
NaN values above, 1075303200 (Wed Jan 28 15:20:00) I got the following 
mail from cron:

** Debug **
NOW=Wed Jan 28 15:20:01 GMT 2004
RRDFILE=/root/rrd/simba-temperature.rrd
UPDATE=N:26:23.0

The script then executes "rrdtool update $RRDFILE $UPDATE".  This same 
script is the one that has put every other value in the RRD.  An 
identical script runs on another machine and I haven't had any errors 
like this at all in the last few weeks it's been running.  I've only 
noticed it on this one machine since installing rrdtool on there this 
morning and starting my data collection.

So if I can be 99% sure that "rrdtool update" was run and 100% sure the 
values fed to it were correct, how come there's NaN in the database?

Thanks,

David

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