[rrd-users] Re: Preventing counter wraps

[Tobias Oetiker]

Today you sent me mail regarding [rrd-users] Re: Preventing counter wraps:

*> 
*> At 12:00 AM 7/5/00 +0200, alex at ergens.op.Het.Net wrote:
*> 
*> >Originally you asked a way around these false wraps.  This should be
*> >done in the front end (perhaps with that "U", perhaps some other way).
*> 
*> I don't know if this has been discussed before or if it is already on the
*> TODO list, but I have been thinking that rrdtool itself should use the
*> sysUpTime of the device to determine the exact time between samples. 
*> 
*> ie: the frontend would query the interface in/out counters AND sysUpTime
*> (in a single SNMP query) then feed this data into rrdtool. RRDTool could
*> use the previous sysUpTime and counter values from the RRD to calculate the
*> bytes/second and store this in the RRA. 
*> 
*> This has the advantage that rrdtool could automatically detect reboots and
*> compensate for it. If RRDTool detected a reboot it could log the
*> bytes/second since reboot based on the value of the counters divided by
*> sysUptime to get the bytes/second since the reboot.
*> 
*> Also, sysUpTime gives us a 10ms sample resolution it would avoid the slight
*> jitter in the 1 second sampling we use at the moment (especially on high
*> latency/unreliable links).
*> 
*> Of course this wouldn't be any use for non SNMP devices which don't have a
*> sysUpTime and COUNTER type data sources, so it would have to be an optional
*> feature...

this has been discussed before ... the only thing I intend to put
into mrtg is the sub-second resolution ... the rest is frontend
stuff as it is device specific ... you can easily store the system
uptime in the frontend and then feed one U to rrdtool as explained
by alex ... 

just think about the overhead ... there is nothing telling rrdtool
which data sources belong to which device ...

cheers
tobi

*> Cheers,
*> 
*> Mike Wright
*> 
*> 
*> 
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*> 

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