[rrd-users] rrdfetch resolution for 15 minute averages returning 5 minute values

[Steve Shipway]

>I am trying to fetch 15 minute averages from an rrdfile created by OpenNMS
>with 5 minute step intervals.  Here is the rrdinfo output for the file:

You cannot fetch data with a 15min interval because the RRD does not have a 15min (3pdp) RRA available.  Therefore, it chooses the best fit with smaller granularity, which is the 5min (1pdp) RRA.

These are the relevant lines of the info (thanks for adding this info with your initial posting!)

rra[0].pdp_per_row = 1
rra[1].pdp_per_row = 12
rra[2].pdp_per_row = 288

This shows that the only available RRAs are 1pdp (5min), 12pdp (1 hour) and 288pdp (1 day).  You would need to create an additional RRA with 3pdp per row to have a 15min average.

If, instead of using 'fetch', you use 'xport', then you can get a 15min average.  This is because 'fetch' will simply output data raw from an RRA, whereas 'xport' can perform calculations (such as amalgamating your data into 15min averages) beforehand, in the same way to what happens when using the 'graph' command.  However, xport has more complex syntax.

Steve

Steve Shipway
University of Auckland ITS
UNIX Systems Design Lead
s.shipway at auckland.ac.nz
Ph: +64 9 373 7599 ext 86487