There was once a case, one disk dropped out of the raid and when the server was loaded in the logs a message was displayed:
md: kicking non-fresh sda1 from array
Since the disk was not in the raid, the data on it was outdated.
First of all, we’ll check the disk for errors, for example, as I wrote in the article below, and try to determine why he was excluded from the raid.
In my case, the disk was completely working, so looking at the information about the raid:
cat /proc/mdstat mdadm --detail /dev/md0
Returned it back to the raid:
mdadm /dev/md0 -a /dev/sda1
After some time, the data was synchronized to disk and the error did not appear any more.