[rrd-users] Bits to Bytes.. trying to figure out what's happening

[Alex van den Bogaerdt]

On Mon, Mar 19, 2007 at 09:31:42AM -0400, Dan Cech wrote:
> Westlake, Simon wrote:
> > In my gig test yesterday, I was hitting between 930 and 970 megs per
> > second on the packet generator, and the 5 minute input/output rate on
> > the switch interface confirmed this to be accurate. However, my graphs
> > show anywhere between 100 and 115 megs. At first, I wondered if it was
> > some type of 'MaxBytes' problem in MRTG, so I changed that value to a
> > very large amount and it didn't rectify it. I then realized that 115
> > megabytes was ~964 megabit.
> 
> Simon,
> 
> ~115Mbps is also around the point where you'll max out 32bit SNMP
> counters with a 1 minute polling interval, as you'll have multiple
> rollovers per minute.
> 
> Are you using 32bit or 64bit (SNMPv2c ifHCInOctets & ifHCOutOctets)
> counters?  If you're not using 64bit counters I'd recommend switching to
> them and suspect it would solve your problem.


Almost agree, except that this happens with a 5 minute polling interval:

2^32 = 4294967296
4294967296 bytes / 300 seconds =  14316557 bytes per second (Bps)
14316557 Bps * 8 bits per byte = 114532456  bits per second (bps)

Temporarily switching to a one minute polling interval (I think
you can keep "step" to 300, no problem):

2^32 = 4294967296
4294967296/60 = 71582788
71582788*8 = 572662304 -> able to monitor 570 Mbps

This buys you some time to see if and how you can use the HC counters.

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