[mrtg] Re: can i keep more data

[Chris Robb]

I'll follow up to this with a correction and a new problem with adding
these rows. The correction is that I mistyped the number of rows to add to
get 2 years of 5-minute data. It should be 209640.

But I've run into a problem with the graphs since performing the RRA
resize. I'm using the rrdcgi program to mimic MRTG's generated graph page.
Here's one:
http://loadrunner.uits.iu.edu/weathermaps/abilene-ngar/mrtg-data/SNVAng-KSCYng/

Notice that the weekly, monthly and daily graphs don't show data past 2.5
days from the current time. I checked the RRDs and the data is there. See:
http://loadrunner.uits.iu.edu/weathermaps/abilene-ngar/rrdviewer.cgi?name=SNVAng-KSCYng&width=500&height=175&startTime=-345600&endTime=-259200
This shows a 24 hour period that occured 4 days before you load the image.

I might understand this better if I knew how RRD chooses which RRA to look
at when creating a graph. 24-hour for yearly? 5-minute for daily? How is
this determined? But even with that info, I'm still not sure I'd
understand it. All the other RRAs (30-minute, 2 hour and daily averages)
have data going back to Sept 23rd, when I started collecting. So, no
matter what RRA it's choosing, it should have data to graph.

The only significant fact about 2.5 days worth of data is that this is the
default length of time that MRTG keeps 5-minute data. As such, it's also
the default the MRTG uses when upsizing the MRTG logfiles to RRD logfiles.
I have the same set of graphs with these defaults that *do* graph the data
past 2.5 days. The only difference is that I added 209640 rows to RRA 0
(5-minute average). Does RRDCGI have some tie to the MRTG defaults in some
way that I'm missing?

Thanks!

-Chris

Chris Robb
Indiana University Global NOC
Abilene/TransPAC Network Engineer
chrobb at iu.edu  Desk: 812-855-8604 Cell: 812-325-8199

On Thu, 24 Oct 2002, Chris Robb wrote:

>
> I saw a few questions that went unanswered to the list on this, so I
> thought I'd share my findings.
>
> When the reference pages refer to "base interval count", this refers
> to RRA 0, as created when upsizing from MRTG to RRD. So, I believe the
> original question was the user wanting to keep 2 years worth of 5 minute
> data. If I'm correct, "RRDRowCount[ezwf]: 210240" will take care of this,
> given a 5 minute polling interval. If you want to do this after the MRTG
> files have been converted to RRD, you have to use the rrdtool resize
> command and add 20640 rows to RRA 0.
>
> When you resize, it adds the rows to "the past". By that, I mean, if you
> do a dump of the rrd file right after you insert rows, you'll see two
> years worth of 5 minute polling intervals with NAN, with only the last 600
> rows containing data. Once you start collecting against that, the new data
> will push out the old data.
>
> Somone asked about changing the other RRAs. Use Resize for that as well.
> Do a "rrdtool info" on the RRD file you want to change and note the RRA
> number you want to insert rows.
>
> Also, the reference mentions that by default upsizing holds about 1 days
> worth of high resolution (5 minutes) of data. Since most people run mrtg
> on a five minute interval, and since there are 600 rows created in RRA 0
> by default, should this be changed to say 2 days with of data?
>
> I just modified the backend to the Abilene Animated Traffic Map to run off
> RRD, which was a pain since our backend is all hacked together. One of
> these days I might be able to share it, if I ever get it cleaned up
> enough. :)
>
> -Chris

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