[rrd-users] Beginner RRDTool question

Andy Riebs andy.riebs at hp.com
Sun Mar 9 21:58:12 CET 2008


This question is raised at least once a week on the list; check the 
archives (see the list at the bottom of mail to this list), and see also 
the excellent rrdtool man pages.

The golden rule of RRD:  RRD will accurately report your data, but it 
will never return exactly the numbers that you entered.

Once you can explain the golden rule, you'll find the people on this 
list to be very helpful.


Sam Crawford wrote:
> Evening all,
> I'm trying to use RRDTool for a network monitoring application I'm 
> receiving data from. The application gives me a bytes/sec reading for 
> active hosts every 5 minutes (note: not all hosts, only active ones).
> My problem is that I might receive a burst of data for one interval and 
> then nothing else for a long time. However, I still want the rrd to 
> record and graph it. But I can't seem to get this working!
> To illustrate:
> rrdtool create --start 1205088000 test.rrd --step 300 
> DS:InOctets:GAUGE:600:0:25000000 DS:OutOctets:GAUGE:600:0:25000000 
> RRA:AVERAGE:0.5:1:600
> rrdtool update test.rrd -t InOctets:OutOctets 1205088300:220041:100
> rrdtool fetch test.rrd AVERAGE -r 300 --start 1205088000 --end 1205088900
> I'm inputting one value and trying to read the value out, but the fetch 
> gives me NaN for the time I input the data. All I want to be able to do 
> is input a value every 5 minutes and read it back. If I don't input a 
> value for a 5 minute interval then I'd want NaN to be recorded.
> I'm sure this is all due to my fundamental misunderstanding of the 
> complexities of the RRA aggregation!
> Thanks,
> Sam

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