----- Original Message ----- From: "Mustafa Abdel-Hady" <[email protected]> To: <[email protected]> Sent: Monday, December 28, 2009 2:41 PM Subject: [mrtg] Fwd: Re: MRTG exact sampling interval
> Dear all, > thanks a lot for your support, I really appreciate that. > This is a part of a MRTG file: > 1256555400 357195 556989 552467 561736 > 1256555100 256331 554642 552467 556445 > 1256554800 145589 552803 189183 558581 > 1256554500 162299 554635 169795 556920 > The difference between time stamps here is 5 min, but you can notice that > there is a big difference between the average and maximum values, which > may mean that there is a certain resolution that is lower than 5 minutes, > or in other words, the MRTG can sense peak utilization values in an > interval which is lower than 5 minutes or it has a polling interval to the > devices less than 5 minutes. > Does that make sense? > And please I want to know this sampling interval. > Thanks a lot. > Best Regards, > Mustafa It's called normalization. Not only is the difference 5 minutes, you will also see that every timestamp is a whole multiple of 5 minutes (300 seconds). Now consider that you are sampling not at 16:00 and 16:05, 16:10 and so on, but are sampling at 16:02, 16:07, 16:12 and so on. MRTG (or rather rateup) will still store it at 16:00, 16:05, 16:10. If the counter value at 16:02 was 100,000 and the same counter was 103,000 at 16:07, then the rate between 16:02 and 16:07 was (103,000-100,000)/(16:07-16:02) = 10. If the rate before 16:02 was zero and the rate after 16:07 was also zero, then you get the following data: between 16:00 and 16:02 rate=0 between 16:02 and 16:05 rate=10 between 16:05 and 16:07 rate=10 between 16:07 and 16:10 rate=0 Rateup combines the first two rates: 120 seconds @ 0/second + 180 seconds @ 10/second = 120*0+180*10 = 1800 per 300 seconds = 6/second. Rateup combines the last two rates: 120 seconds @ 10/second + 180 seconds @ 0/second = 120*10+180*0 = 1200 per 300 seconds = 4/second. Rateup stores: 16:05 average 6 max 10 16:10 average 4 max 10 Now consider the case where 16:07 to 16:12 is not rate 0 but rate 20. between 16:05 and 16:07 rate=10 between 16:07 and 16:10 rate=20 Rateup combines: 120 seconds @ 10/second + 180 seconds @ 20/second = 120*10+180*20 = 4800 per 300 seconds = 12/second. Rateup stores: 16:05 average 6 max 10 16:10 average 12 max 20 Look at the top of your log file. You will see the timestamp MRTG is working with as well as its input. Copy those, look 5 minutes later, copy again, look 5 minutes later, copy again, do the math similar to what I did. It should match. _______________________________________________ mrtg mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/mrtg
