[rrd-users] Re: resize my rrd's

[Alex van den Bogaerdt]

On Thu, Jul 08, 2004 at 02:47:10PM +0200, Andras Horvai wrote:

> Well my fronted create graphs in this manner (focusing --start --end option):
> So, do I have to worry about my graphs?


> Weekly (30 Minute Average)
> /usr/bin/rrdtool graph - \
> --imgformat=PNG \
> --start=-604800 \
> --end=-1800 \

This (and similar) will fail to select the "weekly" RRA in near to 100%
of the time.

The RRA selection mechanism tries to match your request as closely as
possible, and will end up with time ranges such as "2004-07-01 15:40" to
"2004-07-08 15:35".  This will be fetched from the 5-minute RRA, not
from the 30-minute RRA.

Only if the 5-minute RRA hasn't got enough data, the 30-minute RRA will
be the best choice.  Existing rows with "NaN" are quite different from
non-existing rows.  This is why expanding the size of an RRA may yield
surprising results.

Alter the end time to a whole multiple of 1800 (it currently is NOT) and
this will overcome the problem.  Note that "-1800" is "now-1800" which is
not a multiple of 1800 in most cases.

HTH
Alex

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