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

Simon Hobson linux at thehobsons.co.uk
Tue Jun 7 12:11:10 CEST 2011

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

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