Steve, Completely agreed that there would be a difference but the 700-800Mbps usage is pretty sustained. I don't think it is simply the averaging over the interval that is causing the huge discrepancy.
I misspoke in the earlier email - it is running on 5 minutes in cron. However, I've been watching it today and it is taking significantly longer than 5 minutes to complete. So I believe this is a likely candidate - the interval is set 5 minutes but it is actually only completing a run once every 15-20 minutes. I'm going to try changing the interval to a much larger value tonight, dumping the RRDs and setting cron to a value that it is actually able to complete. On Wed, May 15, 2013 at 3:12 PM, Steve Shipway <[email protected]>wrote: > >(Cacti is running on 1 minute, MRTG is running on 10 minutes.) > > And here we have the explanation. > > If MRTG is only polling every 10min (and you have the wrong Interval in > the cfg file and in your RRD file for this) then it will be, in effect, > giving you a 10min average speed for the port. > > Cacti, on the other hand, is polling every 1min and so is giving you 1min > averages. > > Therefore, the MRTG graph will be much more smoothed out and flatter, and > Cacti's graph will be more spiky, showing higher peaks for bursts of > traffic that are relevant in a 1min interval but not over a 10min > interval. This is why you see much higher values in Cacti. The same > effect happens in MRTG if you compare the peaks on a 5min average graph > (daily) and on the 2hour average graph (monthly). > > Consider this set of 1-minute interval data: > > 10 > 1 > 1 > 1 > 1 > 1 > 1 > 1 > 1 > 1 > > This is a 10min sample; for MRTG it would see a total of 19, IE 1.9/min. > Cacti, however, would see them all, and show a graph with a spike up to > 10. Therefore, very different graphs. > > If you want them to match, you will need to change the MRTG Interval to 1 > minute, recreate your RRD files, and poll every minute - and change your > PHP graphing script to take account of the higher granularity of data > available. > > Steve > > *Steve Shipway* > University of Auckland ITS > *UNIX Systems Design Lead* > [email protected] > Ph: +64 9 373 7599 ext 86487 > **Voice: (414) 810-6392 > -- - Simon Westlake [ digitalgunfire.com ] AIM: ShirowDG ICQ: 2227213 Voice: (414) 810-6392
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