[rrd-users] Re: add upper and lower limit lines?

[Alex van den Bogaerdt]

On Mon, Oct 23, 2006 at 02:50:25PM -0700, Rob Newman wrote:
> Hi RRD users,
> 
> In one of my RRD graphs I would like to draw lines of maximum and  
> minimum valid value. I have a gauge variable that varies greatly, and  
> I want to add a maximum line at +40, and a minimum line at -40. This  
> way, anyone who looks at the graph can see if the value plotted from  
> the archive is valid or not. I know I can do this with RRD. From the  
> documentation (http://oss.oetiker.ch/rrdtool/doc/ 
> rrdgraph_rpn.en.html) I see that I can define a VDEF expression.  

I'm not sure what you are trying to do.

Anyway: if you only want lines at +40 and -40, use HRULE.
If you want to limit your values, remove spikes, then CDEF should
be used. Example can be found in the tutorial.

VDEF is used to get a property of the data set, for instance:

DEF:mydata=file.rrd:....
VDEF:themaximum=mydata,MAXIMUM

This will make "themaximum" available, which you don't want.


-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/

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