[rrd-users] Re: Graphs wrong after reboot - samples included

[Alex van den Bogaerdt]

George Dau wrote:

> No, setting maximum values for the counters is not a complete solution. If
> the counters get reset when the value of the counter is high, you will get a
> wrap that produces a wrong result that is also less than the maximum you set
> and thus will be recorded as a value. You still get wrong data in your
> database.

This is correct.  Using the limits as I described reduces the problem
and I only consider this to be a workaround.

The only real solution is to implement #1, which can be difficult if
not (next to) impossible.

> I went with the DERIVE data type. You miss one entry when there is a counter
> wrap, which for me is better than having a wrong entry. I put quite a bit of
> testing and thought in to this, and DERIVE is definitly the best for my
> data.

This may indeed be a better workaround.  Keep in mind that:
1) You still need to set the lower limit to 0 if I'm not mistaking
2) You need to prepare for the unknown interval.  If accurate data
   is your primary concern, you should *not* let rrdtool handle this
   and xff should be 0.

Use rrdtool tune to alter the properties of the existing database.
rrdtool tune rl0.rrd \
     -d input:DERIVE \
     -i input:0 \
     -d output:DERIVE \
     -i output:0

I'm not sure if you can specify multiple changes (and are too lazy right
now to check for myself) so you may need to use the tune command four times.

cheers,
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