[rrd-users] rrd evaluate by number

[Alex van den Bogaerdt]

> my rrd contains three rows: "octets_in", "octets_out" and "snr" captured
> from a wireless router.
> Is it possible by using of rrdfetch to get the difference of the last week
> by octets? Or must I write me a shell script myself and make the differece
> from the actual timestamp to a timestamp one week ago? Bu how can I find 
> the
> exact timestamp one week ago?
>
> My goal is to get the traffic (octets) of the last week by number.


Then forget about fetch, use graph.

total == average * time.

Make sure to understand how rrdtool consolidation works.
( http://www.vandenbogaerdt.nl/rrdtool/ )
Make sure to ask for existing timestamps in a suitable RRA. An RRA which 
stores one hour per CDP would be nice, you can ask for midnight to midnight. 
If you use an RRA which stores one day per CDP, you need to ask for 00:00 
UTC to 00:00 UTC (2am in winter, 3am in summer).

You can get the average using rrdtool graph, PRINT (to get the number) or 
GPRINT (to get it on screen)
You know the time to be one week, which is 604800 seconds.
If you first multiply and then let rrdtool compute the average, that's okay

CDEF:tmp1=octets_in,604800,*
PRINT:tmp1:%6.2lf

and so on.