[rrd-users] Question with 1-hour samples

Jason iknowjason at pobox.com
Wed Jan 19 19:01:49 CET 2011

On 01/19/2011 03:08 AM, Simon Hobson wrote:
Dunno ! We've zero idea what values you put in and when, or what you got

Can you post an example showing what updates you put in, and what you
get out. That means showing us the rrdtool update commands to see
what went in, and show the stored data obtained with rrdtool fetch.

Simon, thanks a million for your response, mate.  I'm very excited about
RRDTool and learning its various applications.  I will get you the
detailed answers for what data I put in but I have a question.  I'd
really like to make sure first that I'm understanding how the data works
and the max CF.

This is my update command, which runs every 5 minutes from a perl script
via Linux cron:
RRDS::update("alerts.rrd", "N:$val");

With the two following 1 Hour RRAs for the DS (only posting relevant
data), this is how the RRDTool create creates the RRD:

Is my thinking correct here that this will take a 1 hour average of 12
5-minute samples.  So each Consolidated Data Point is 1 hour.  The first
RRA will be stored 336 rows/hours (14 Days), and the second RRA will be
stored for 1440 rows/hours (60 days)?

Now let's say my data updates after the first 3 hours of the following CDPs:
(20, 40, 30)

Wouldn't this mean that the MAX Consolidation Function will return 40 as
the Maximum average for that 1 hour, for both 14 days of store, or 60
days of storage?  This is what I'm assuming, but maybe I am wrong.

This is what the graphing function is doing:

GPRINT:alerthouravg:MAX:Maximum alerts per hour\\:  %6.2lf
AREA:alerthouravg#1E90FF:Average per Hour

When the data graphs, it shows what I wouldn't expect.  For the 60 days
of storage graph, the Maximum average shows up as a lower value (20),
and the 14 days of storage graph shows a higher value (40).  This makes
no sense to me.  Am I correct in my assumption that for the sample
stored data above, they should both graph / gprint that the Max 1-hour
average is 40?  What am I missing in this example?  If I am correct,
then perhaps it's a different problem with how the data is being
inserted in.

In my real data:
The 14 Day graph shows / prints the Maximum alerts per hour of 122,729
while the 60 day graph shows / print the Maximum alerts per hour of

I will fetch out the real data, but can you please help me in confirming
that this is correct, or I'm off base on my assumption with the sample
data?  I spent a week and a half purely reading the tutorials and
documentation, testing the detailed examples, to make sure I understood
the concepts, theories, and principles behind RRDTool.  I want to make
sure that I understand how it is supposed to work exhaustively.  I can't
find this answer in any of the sample documents, so that's why I'm
asking this list.   Thank you for your help.


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