[rrd-users] Re: Newbie questions..

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Wed Feb 14 12:21:02 MET 2001

Lyon Lee wrote:

> I'm just trying to get RRD off the ground..
> The data i'm putting in is basically ping data for some wireless devices to
> monitor the speed of the wireless network.
> STATUS  TIME       OUT				IN		     dB
> GREEN    30   2001-02-13_16:30:01   2001-02-13_16:30:31   -89   982103401
> GREEN    43   2001-02-13_16:33:00   2001-02-13_16:33:43   -89   982103580
> Time is in seconds, and the only data I'm putting in is the time sent out,
> and the delta time.

If I understand you correctly, you end up with command like
   rrdtool update bmrg-tor1.rrd 982103401:30
   rrdtool update bmrg-tor1.rrd 982103580:43

This is fine, as long as the updates come in chronological order.
However, RRDtool will consider the data at 982103401 to be valid
for the interval *before* 982103401 (so: 982103340..982103400) and
not the interval from 982103340..982103400 (which is what you are

If possible, update with (TS+TIME):(TIME), again in chronological order.

> rrdtool create bmrg-tor1.rrd 
> --start 982100700 -s 60 
> DS:tor1:GAUGE:8000:1:8000 
> RRA:AVERAGE:0.5:1:1440

This looks OK.  You start your database at Tue Feb 13 21:45:00 2001 UTC.
The step time is 60 seconds and the DS is called tor1. Samples put into
the database may be 8000 seconds apart (over two hours) and the maximum
is set to 8000 seconds.  The RRA you defined will have one day worth of
data as you have one PDP (your step time) per CDP (row in the RRA).

> Problem:  I'm getting nan's like crazy.  Thats all I get when I do a 
> rrdtool fetch bmrg-tor1.rrd AVERAGE..  but i'm thinking its cause of the
> AVERAGE RRA i've setup.

I think it might be because you are checking well after you did the
last update.

>  982105560: nan
> [...]
>  982106160: nan

This is Tue Feb 13 23:06:00 2001 UTC to Tue Feb 13 23:16:00 2001 UTC
but your update examples show other times.

982103401 is Tue Feb 13 22:30:01 2001 UTC and this is your first
update (at least: AFAIK). That means that the whole database until
that moment will be filled with NaN.  After a few updates, you
will (or: should) get known data in your database but only at the

Try "rrdtool dump bmrg-tor1.rrd > bmrg-tor1.xml" and view the content
of the database.

> Questions:
> Is it possible to get rrdtool fetch to just show me the RAW data (since its
> a gauge)?

No, since it is not available.  Check the mail archives and focus on
data resampling, consolidating, interpolation.

> Does RRD not accept data in sequential order?
> ie:  If i have a TS of say, 100 and 160, and i input data for 160, THEN 100,
> will it chuck the 100 out the window?

? TS is your time stamp in seconds since the epoch?!?  This needs to be
far more than 160.  But yes, you should get an error if you try to enter
data in the RRD that already exists.  If you enter data for "now" then
every slot before "now" will also automatically be filled.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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| http://faq.mrtg.org/                                                 |
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