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

[Tobias Oetiker]

Today Dan McGinn-Combs wrote:

 |
 | 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
 | seconds)
 |  - if it takes 10 minutes (600 seconds) to get a reading, leave it at
 | undefined
 |  - 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

perfect


 | 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?)

right ... except that you there is no 'official' way to add an RRA
... you have to decide when you create the RRD.

 | 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 know?")

in DEF you tell what kind of data you need AVERAGE / MAX / ...
together with the resolution of the graph and the desired timeframe
rrdtool identifies the RRA which is best suited to deliver the
data.

 |
 | 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).

you could try using the log scale. CDEF is certainly also an option

 |
 | 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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