Munin: Why is the utilization by month higher than by year?

I just learned about Munin and I checked out some example diagramms. I don't get how the utilization by month is at about 60% and the utilization by year says its bellow around 10%. I would expect that the second diagramm should also have 60% utilization, just that the peaks are much more since the range of the x-axis is 12 times bigger.

What did I misunderstand?

EDIT: Maybe I should mention that /dev/sda is a part of a RAID 5.

Solution 1:

The base tool used by Munin is rrdtool and this works by averaging down values for longer time periods. It records actual measured values eg. once every 5 minutes for a day (and then starts overwriting older values, hence "round robin"), and then derive an average of 12 of those values down to an one-hour resolution that it keeps for 30 days and maybe further average 24 of those to a day to keep for a year.

If you do this, your peaks naturally will get smaller and you will loose details. This is a tradeoff to keep databases small, but in many cases, you just don't need these details. If you do, you have to either reconfigure your monitor tool or use something else entirely.