Help understanding rrdtool hourly, daily, weekly, etc

bt101 · 06-25-2011, 06:48 PM

I want to record temperatures every minute.
I would like to display graphs of the temperature that would include:

raw (every minute)
daily min/max/avg

When you define an RRA, you specify:

how many raw values make up the RRA
how many RRA values to keep

So, if I specify an RRA that has 60 * 24 = 1440 samples (one day's worth) how do I know what window is being used?

For example, I need min/max/avg values that go from midnight to midnight (the information does not make sense otherwise). In the RRA, there seems to be no way to specify where the window starts/stops. Does it just choose some random window (for example from 14:47 one day to 14:47 the next day)?

norbert74 · 06-27-2011, 06:25 AM

As far as I know the window is set by the start time (--start) and the step (--step) defined in the rrd, you cannot set this for each rra individually if they are in the same database. What you probably need is something like this:

Code:

rrdtool create temperature.rrd 
--start 1293861600       (start at midnight, a utc value)
--step 60                (every minute the database expects a new entry) 
DS:temp:GAUGE:120:0:100  (define a datasource, name it temp, use the absolute value, if there is no data for 120 seconds insert UNKNOWN, min. allowed value is 0, max. allowed value is 100)
RRA:LAST:0.5:1:1440       (save the absolute value every minute for one day: the LAST value of 1 primary data point is the absolute value, thus no consolidation)
RRA:MIN:0.5:1440:7    (save the daily minimum for one week: MIN of 1440 primary data points, 7 times)
RRA:MAX:0.5:1440:7    (save the daily maximum for one week)
RRA:AVERAGE:0.5:1440:7    (save the daily average for one week)

bt101 · 06-29-2011, 08:37 PM

Ah good tip. Thanks I'll give it a try.

I guess that all subsequent hours would line-up properly.
Days would work also (if you start at a time that has an offset for your timezone) however I would imagine days would get messed up when the clock switches between standard and daylight saving time.