The rrd databases get written to every minute, this adds up to around 100 Megabytes written per hour.
Per default linux writes data to disk after a maximum of 30 seconds in the cache.
Increasing this to 10 minutes reduces actual disk writes to around 10 Megabytes per hour.
Don’t change this if you handle data on the Raspberry Pi which you can’t lose the last 10 minutes of.
Increasing this write delay to 10 minutes can be done like this (takes effect after reboot):
sudo cat >/etc/sysctl.d/07-dirty.conf <<EOF
vm.dirty_ratio = 40
vm.dirty_background_ratio = 30
vm.dirty_expire_centisecs = 60000
EOF
It’s not that critical though modern sd-cards should handle that amount of written data for 5 years easily 