[rrd-users] Re: Counter reset to zero question

[Alex van den Bogaerdt]

On Thu, Jul 01, 2004 at 11:20:56AM -0700, Jack Tavares wrote:

> when the box gets reset, the counters go to zero.
> and then start to rise again.
> 
> I can set a MAX value when computing the CDEF, but 
> I was wondering if there was a better way to do this?

Yes.  First of all, rates above the maximum will never make
it into the RRAs.  Use that to your advantage and do set
a maximum.

Secondly:  make sure RRDtool gets valid input.  When you give
a counter value to RRDtool, you are saying: "This is the new
value.  Use it together with the previous one to compute a
rate".

When a reset occurs, the previous value is zero, and its
timestamp is the time at which the boot occured.  Make sure
RRDtool knows this.  To do so, you have to insert the value 0
with an appropriate timestamp.

When you do this, you have the same problem: The previous
value (before zero) isn't correct.  Most likely you don't
know what it was:  The value at (boottime-1) is "U" (unknown).
Insert that as well.

You will miss one interval: The one between the last known
poll before boot and boot itself.

Alternatively, you can just enter "U" one second before the
first update after boot.  Doing so will mean you miss two
additional intervals.

HTH
Alex

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