[rrd-users] RRA:AVERAGE - How does RRDtool know which RRA to use?
linux at thehobsons.co.uk
Wed Aug 18 22:00:09 CEST 2010
>Let´s say I plot a graph from "now" to -1month, does RRDtool "automatically"
>use "no 3", or do i specify it somewhere?
>"no 1": 600 samples of 5 minutes (2 days and 2 hours)
>"no 2": 700 samples of 30 minutes (2 days and 2 hours, plus 12.5 days)
>"no 3": 775 samples of 2 hours (above + 50 days)
>"no 4": 797 samples of 1 day (above + 732 days, rounded up to 797)
Best to be more accurate in your start and end times.
For starters, don't end "now", end "now - (now %
interval)" where interval is the period for the
consolidation you want to use. Taking your
example, you would only ever use 00:00, 02:00,
04:00, and so on for your monthly graph.
For start time, again be precise. I will select
"end time - (interval * number of pixels)" so
that the start time is exactly on a period
boundary and each sample fits to one pixel in the
For the consolidations you've used there it won't
happen, but there are some combinations that can
cause you to get low resolution data. rrd tool
will use whichever consolidation provides the
most data to fill your graph - so if you manage
to have odd periods you may find your one day
graph drawn with data consolidated at one day !
As a simple example, suppose you have
consolidations at 10 minute and 25 minute
resolutions. For some values of "now", there will
be a more recent value in the 25 minute
consolidation than the 10 minute one. Eg, if they
happen to coincide at midnight, then between
00:25 and 00:30 this would be the case.
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