[rrd-users] Re: Displayed data in rrdgraph is not the same as the input data

[Peter Valdemar Mørch]

Judith L. Pancho judith.pancho-at-latitudebroadband.com |Lists| wrote:
> I'm using rrdtool to monitor the network traffic. But there seems to be 
> a problem. The input data is the throughput in kbps. I converted this to 
> bps (by multiplying 1000) and entered the data in rrdtable. Then I used 
> rrdgraph to display the CURRENT throughput. I expect that the CURRENT 
> throughput would be the same as the input data but  the CURRENT 
> throughput (in kbps) displayed in rrdgraph is different from the input 
> data. 
> 
> Your help would be greatly appreciated.

Hi Judith,

If you update your rrd file exactly on step boundaries, the output data 
will be exactly your input data. So if you want your output data exacly, 
make sure your timestamp on update is exactly e.g. 12:00:00 and not 
12:00:02.

When the update timestamp is slightly off, rrdtool compensates the input 
value for that, because internally it doesn't store your update time. 
So, in effect, rrdtool compensates for my sloppy system where cron jobs 
don't run EXACTLY on time. That is probably why you don't see your input 
values exactly on output.

Peter

-- 
Peter Valdemar Mørch
http://www.morch.com

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