that went ... not too well xD
Well mdadm decided to have a moment. I got the server operational again after rebuilding the raid1. But the big raid5 also does not be toooo happy when booting up.
After waiting a bit and the machine booted but the raid was not assembled. I can assemble manually and mount it. So its running again.
But rebooting it makes the same thing happen.
having a homeserver is fun they said! All will be fine they said!