[rrd-users] Re: DST beginner question

[Daniel Tepas]

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I'm not an expert, but here's my 5 cents....

Christoph Schwabl wrote:

>
> I have a file where I can find my values (atm cells). This are
> already *DELTA* values in atm cells, so I know that COUNTER is the
> wrong DST.
>
> I want to build a graph in bits/s.
>
> Do I need DERIVE, GAUGE or ABSOLUTE for the DST.
>
I _GUESS_ it's gauge you need. Absolute is definitively wrong, because
it has nothing to do with a value per second.

> I know: 1 atm cell = 53 byte = 424 bit. So I sent to the rrd
> database (file) the value*424.

> But I always get a graph width very high values which could not be
> correct (I have this problem when I use DERIVE, GAUGE or ABSOLUTE).
>
How do you get the values in the rrd? Maybe the script is faulty, have
you checked? Are the values in the rrd file correct? Check this! You
have to point if the fault happens before putting the values in the
rrd or while processing the rrd.

> I know it is not correct because I can also check the throughput
> with mrtg from a other device. Could it be, that the rrd tool can
> not calculate from the value*424 bit (ca. 900s value) to bit/s?
>
No, I don't think so. That's what rrd is made for. mrtg is using rrd
too, by the way.

> It is also important that I do not get always exact 15min (900s)
> values. e.g. I get 905, 890, ... values. But I have the exact time
> which I can sent to my rrd database (file). Is this a problem when
> I update the database not exact with 900s updates?
>
No, it is not. You may get inaccurate values for short time periods,
but this is quite clear. If you poke values in your rrd approx. 15
minutes you don't expect exact values all 5 minutes. But for, let's
say, a few hours, it should be exact.

> PS: I have used the following rrdcommands with a perl script:
>
> $rrdtool create $directory_file --start $unixtime_new --step
> $step_sec DS:input:ABSOLUTE:$step_sec:U:U
> DS:output:ABSOLUTE:$step_sec:U:URRA:AVERAGE:0.5:1:8640
>
> and for update
>
> $rrdtool update $directory_file $unixtime:$value_in:$value_out
>
Do $value_in and $value_out contain both, input AND output?

Regards, Daniel
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