[rrd-users] Re: strange beavior

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Sun Feb 3 16:56:22 MET 2002

Un L'Unique wrote:
> > > Bug or misunderstanding ?
> >
> > Well, mrtg contains a datastore of constant lenght. If you define
> > an RRA of 2 years length, and have a start time of "now" the
> > 'newest' data in the RRA will be 'now' and the 'oldest' from two
> > years ago ... as rrdtool does not know the data from 2 years ago it
> > is set to 'unknown'

> Well I find this surprising: why does rrdtool agreed to give me answer for
> something before the --start time ?

You will *always* get an answer.   If the data is not in the database,
the answer will be "I don't know"  (thus: Unknown which is NaN).

> Anayway, my database is 1 year lenght and I am able to fetch from 1990. I
> also got data from 1997 in the dump makeing it very large. ( after removing
> pre 2002 line, le dump shrink from 500MB to 11MB )

Use "rrdtool info" on your database.  This shows you what the database
will store.  Important numbers (for this subject) are:
   "step = 300"                the number of seconds per PDP
   "last_update = 1012751100"  the end of the database
   "ds[ds0]" and ds[ds1]       the number of DSes
   "rra[0]" .. "rra[7]"        the number of RRAs
   "rra[7].rows = 800"         the number of rows in each RRA
   "rra[7].pdp_per_row = 288"  the number of PDPs in each row

If "pdp_per_row" is 288 and "step" is 300, each row is 288*300 seconds
in length.  This is 86400 seconds equalling 1 day.  There are 800 of
such rows so this RRA stores 800 days ending at time 1012751100.

The number of elements in the database dump file is related to the
number of RRAs, the number of rows in each of those RRAs and the number
of DSes in each row.  I have no problem whatsoever to work with databases
that contain 800 rows per RRA, 8 RRAs per database, 2 DSes per row.
This means 800*8 lines and some change in an xml file.  The xml file is
about 600 KB of size.  Should this have to become a file of 500 MB,
I would need to store 20 DSes for 10 years or so ...

I think you're doing something that you shouldn't be doing.  Restart
from scratch, start simple and try to understand rrdtool before
continuing with more difficult stuff.  Use the tutorial.

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