[rrd-users] Ok, just a couple more questions <g>

Dan McGinn-Combs d.mcginn-combs at mindspring.com
Sat Feb 24 17:49:16 MET 2001

I've read the tutorial (three times... not counting the countless referals
to the examples). I've read the MAN pages (several times each). I think I
have it. But I have just a couple more questions.

a) If I create a DS (say DS:temp:GAUGE:600:0:100) and then set up an
RRA:AVERAGE:0.5:4:200, what I have said is:
For the DS -
 - I want to store temp as a gauge (i.e. don't divide readings by 300
 - if it takes 10 minutes (600 seconds) to get a reading, leave it at
 - it should be between 0 and 100 degrees.

For the RRA -
 - wait until you get four readings
 - average them
 - if half of them are unknown, treat the average as unknown
 - keep 200 averages in the file


b) If I change (or add) to RRA:MAX:0.5:4:200 the only thing that changes is
the "average them" part and it keeps the maximum reading of the four,
disgarding any unknowns (up to two). (right?)

c) In a graph, there is a comment somewhere in the MAN pages or the tutorial
which says that RRDTool will figure out which RRA to use. Hmmm.... how does
it know? There doesn't seem to be a way to tell it apart from identifying
"AVERAGE" or "MAX." (this is my favorite computer question: "how do it

d) If I have two data sources where one is perpetually small (in the 10 to
20 range) and the other is perpetually large (in the 800 to 1200 range), is
there a clever way to display them together so that the small one is visible
while the large one is as well? Is the best way to do this to set the range
of the graph or to use a CDEF function and show proportions? (this is
perhaps just a usage question, and not for the main topic, but I'm calling
on the vast experience out there).

Ah, well you all are the experts. Thanks for your assistance......

Dan McGinn-Combs
d.mcginn-combs at mindspring.com
Atlanta, Georgia

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