[rrd-developers] Re: Restarting devices

[Tobias Oetiker]

Today you sent me mail regarding [rrd-developers] Re: Restarting devices:

*> Tobi,
*> 
*> > what would that buy you, knowing the 'last' value ? RRD knows it
*> internally,
*> > so if there is anything interessting we can do with it, let me know ...
*> > RRD already checks if it is smaller than the last value recorded ...
*> 
*> What happens if at time t-1 I read the value 1000 from my router ifInOctets
*> via SNMP. At time t I read 500... the counter is suposed to behave as an
*> increasing value... how will RRDtool handle that? Will it store NaN?

yes unless -500+2^32-1 / 1 or -500+2^64-1 / 1  is between the two border
values specified for the DS ...


*> I had the same spike problems that Bert Driehuis had when the equipment is
*> reset, which makes all my graphs unusable. Yes, I can force the min and max
*> with 0 and the ifSpeed value, but it might not work all the time. Some
*> spikes might appear.

sure ... 

*> What should I do? My idea was to check manually if the current value is
*> lower than the last value, and then store a NaN in this case.

you could use the 'DERIVE' data type this is like counter but does not do
any COUNT overflow magic, so if you give a min value of 0 you will get NaN
for most of your resets ... another nice aporoch is to monitor the uptime of
your equipment and store a U everytime you find that the device got reset
...

cheers
tobi

*> 
*> Best Regards,
*> Luis F Balbinot
*> 
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