Since some days, I noticed that "resync" of md device triggers at boot time.
Sometimes, it triggers at every boot.
It slows down the computer and the disks access for 90minutes.
I didn't notice this kind of behavior at the beginning.
Lately I didn't change anything except changing a component (PCI sound card) and keeping the OS up to date by installing the last updates.
So I checked the health of the disks (with smartctl) and manually triggered a check of the array (with /usr/share/mdadm/checkarray).
But everything looks good.
In the log (first post) there are messages about the bitmap of the array and that is not clean forcing a reconstruction of the array.
I don't think it's normal.