FYI:

altair usr # mdadm /dev/md0 --manage --add /dev/sdc1
mdadm: add new device failed for /dev/sdc1 as 3: Invalid argument
altair usr # grep md_import_device /var/log/messages | tail -1
May 20 15:53:37 altair kernel: md: md_import_device returned -22
altair usr # mdadm --version
mdadm - v3.2.4 - 9th May 2012

Solution:

altair usr # echo "=sys-fs/ ( Read more... )