OK - point taken - this is what I get for posting quickly. I was only considering a simple RRA where 1cdp=1dp, so you can do an on-the-fly calculation over a range on a calculated value. Slow, but it works.
The issue hits when you're working on a rolled-up RRA where 1cdp = x dp where x>1, since then you get max ( a-b ) = max ( avgX(x) - avgX(b) ) and you're stuffed by a greater degree as X increases. I should have remembered this as it is what messes up my 95th percentile calcs on RRD files that only have MIN/MAX and AVG RRAs as the granularity decreases. I still favour storing the a and b values for future use, but to get max(a-b) accurately over rolled-up RRAs you'll need to store a-b as well. Steve Steve Shipway University of Auckland ITS UNIX Systems Design Lead s.ship...@auckland.ac.nz Ph: +64 9 373 7599 ext 86487 _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
