How to change RRD parameters?

[dexx]

I can see where in Cacti i can change how RRD records stats. ie management > data sources > RRAs. If i want to change the 'weekly' archive to use 5 minute averages, i can do it here. However i cant see how to actually make RRD use these revised settings. When i go and look at the weekly data, its still using 30 minute averages. How do i make RRD start using the modified settings?

[gandalf]

Changes to a data template are not propagated to existing rrd files. This is mainly due to rrdtool not allowing those changes.

The change you're heading at is kinda broken. This is mainly due to cacti making a non-existing correlation between rra settings and graph timespan. RRDTool only is interested in RRA setting, not the timespan. And neither cacti nor rrdtool in fact correlate a graph's timespan to any rra. Instead, rrdtool auto-selects the "best-matching rra" for a given graph's timespan.

I take it, that you do want to be able to zoom into a graph up to a 5 min interval's granularity not only for past 2 days (which is default) but for past 7 (or 10?) days.
This can be done when increasing the "Rows" of the RRA defining the 5 min granularity (that is the one usually called "Daily"). There's a script that does this, published at 1st link of my sig, chapter on rrdtool.

Of course you should change the data template as well for all new data sources to be created.
R.

[dexx]

I think i'm still missing something here. I tried updating the data template and creating a new graph (therefore new RRA source). Its been running for a few weeks. When i do a CSV export of the data spanning the 3 weeks, it shows a 30 minute granularity. I had redefined the data source so that granularity should be:
hourly (1 min avg)
daily (1 min avg)
weekly (5 min avg)
monthly (5 min avg)
yearly (1 hour avg)

Is there some documentation which details exactly how to set (or redefine) granularity?

[gandalf]

I think i'm still missing something here. I tried updating the data template and creating a new graph (therefore new RRA source). Its been running for a few weeks. When i do a CSV export of the data spanning the 3 weeks, it shows a 30 minute granularity. I had redefined the data source so that granularity should be:
hourly (1 min avg)
daily (1 min avg)
weekly (5 min avg)
monthly (5 min avg)
yearly (1 hour avg)

Is there some documentation which details exactly how to set (or redefine) granularity?

Using same granularity more than once is bad. At least, it's a waste of space and perhaps makes rrdtool throw errors or behave wrong. Find some hints at 1st link of my sig
R.