with RRDtool the older your data is the less of it you have. You might be logging at 1s period, and you get a nice graph for the last year, but if you want to

with RRDtool the older your data is the less of it you have. You might be logging at 1s period, and you get a nice graph for the last year, but if you want to look back at a 1 minute period from a year ago your 60 samples are gone and have been aggregated. Historians like Pi etc will 'compress' time series by only storing data points where data has changed by some threshold. If you look back 5 years all the resolution is still there.