[rrd-users] Re: create rrd files - basic questions

[Alex van den Bogaerdt]

On Tue, Sep 17, 2002 at 11:14:05AM -0300, Augusto Castelan Carlson wrote:

> -In the DS configuration option, if I´m going do graph bits traffic, the 
> ´min´and ´max I put in bits (example: 10000000 for 10Mbps)?

Don't think bits or bytes.  RRDtool has no concept of it.  Just
look at the numbers you're going to *input*.  RRDtool will always
"change" your input to a rate, no matter what you insert.

GAUGE: the number already is a rate -> don't change
COUNTER: compute the rate by dividing delta(counter) through
delta(timestamp).
(more DS types in the docs and the tutorial)

The rate is what's going to be checked against the max. value
(and the min. value by the way).

If your numbers are already bits then for a 10Mbps interface
the maximum rate will be 10,000,000.  If the numbers are octets
then the maximum rate will be 10,000,000/8.

[note: changed order of questions]

> -The manual (rrdtool create) do not explain what is primary data point 
> (PDP), and this option became not clear for me.  What doc explain what 
> is PDP?

Primary data point.  After computing the rate, RRDtool will compute
a normalized interval w/ rate.  See faq.mrtg.org
Also lookup CDP (consolidated data point) when you're there.

> -In the configuration option RRA, I did not understant how to use the CF 
> option and when?

see the tutorial, the docs and faq.mrtg.org
Basically it is this:

min(1,2,3,4,5) --> 1
avg(1,2,3,4,5) --> 3
max(1,2,3,4,5) --> 5

It has to do with consolidating more than one PDP into a CDP (see below)

> - For the xff option, I did not understant what really is this factor 
> (may you can give an example) and what is the factor I need to use.

One or more PDPs will be combined to create one CDP.  If more than one
PDP is needed per CDP, chances are one or more will be unknown.  xff is
a factor that is allowed to be unknown.  Think percentage but divide
this percentage by 100.

Example:  if you need 6 PDPs to create one PDP and if xff is 0.5 then
50% of the PDPs may be NaN and still produce a valid CDP.  One more
value is NaN then the CDP also becomes NaN.

> -Assuming the I´m collecting some data every 300 seconds. If I want to 
> store for 24 hours, I hato put as value for the option rows a number 
> that multiplied for 300 seconds give me 24 hours in seconds? In the 
> manual, the example put 1200 * 300 = 1000hours.  THe number 1200 is the 
> number that I cited above?

The duration of each PDP (--step 300) times the amount of PDPs per CDP
(RRA:....6....) is the amount of seconds per CDP.  The amount of CDPs
in the database (RRA:....1200) times the amount of time per CDP is the
total amount of time available *in that RRA*.

You can have more than one RRA.

The tutorial explains this; also look in the archives of this list.

HTH
Alex

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