[rrd-users] gap in graph in case of UNKNOWN value

Martin T m4rtntns at gmail.com
Fri Jun 10 00:17:54 CEST 2011

I'm sure it's showing zeros- when the network outage started, HDD
temperature value went from previous value directly to zero. If I had
a network outage and server was unreachable to a machine where
rrdtools runs, following data was written to RRD:

# rrdtool fetch HDD.rrd AVERAGE -s 1307061000 -e 1307075400

1307061600: 2.8986899863e+01
1307062800: 0.0000000000e+00
1307064000: 0.0000000000e+00
1307065200: 0.0000000000e+00
1307066400: 0.0000000000e+00
1307067600: 0.0000000000e+00
1307068800: 0.0000000000e+00
1307070000: 0.0000000000e+00
1307071200: 0.0000000000e+00
1307072400: 0.0000000000e+00
1307073600: 0.0000000000e+00
1307074800: 1.0011661112e+01
1307076000: 3.3748035371e+01

1307061600 is just before the outage and outage was over since
1307074800. RRD was made with a following command:

rrdtool create HDD.rrd \
--step '60' \
'DS:HDD:GAUGE:120:0:150' \
'RRA:AVERAGE:0.5:2:1440' \

If any additional information is needed, please ask!

Am I correct, that in my case there are zeros written to the RRD in
case of UNKNOWN value? If yes, how to change this behavior?


2011/6/7 Simon Hobson <linux at thehobsons.co.uk>:
> Martin T wrote:
>>I have a RRD database with a step of 60s and heartbeat of 120s. This
>>database holds the GAUGE value(HDD temperature of my server). There is
>>a script which asks temperature value from the server after every 60s
>>and updates the database file. Finally I have a "rrdtool graph"
>>script, which draws the graph. Problem is that in case the server is
>>not reachable to the machine where rrdtool runs and UNKNOWN value is
>>written to the RRD database, there is no blank gap on the graph.
>>Instead it looks like the temperature value is assumed to be "0". What
>>might cause this?
> How are you graphing (ie what is the graph command) ?
> Are you sure it's showing zero and not a gap ?
> Are you sure you are writing unknowns and not zeroes to the database
> OR are not writing anything ?
> With the values given, after 2 minutes you should see unknown in the
> database PROVIDED you are either not writing data, or are writing
> "unknown" as the value.
> --
> Simon Hobson
> Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
> author Gladys Hobson. Novels - poetry - short stories - ideal as
> Christmas stocking fillers. Some available as e-books.
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