Create A RAID-1 Array mdadm --create /dev/md0 --level=1 /dev/sda /dev/sdb

Scan For Disks mdadm --detail --scan

Add Disks To mdadm.conf mdadm --detail --scan >> /etc/mdadm/mdadm.conf

Check Status cat /proc/mdstat

Mark Disk as Failed mdadm --manage /dev/md0 --remove /dev/sda

Remove Failed Drive mdadm --manage /dev/md0 --fail /dev/sda

Add Disk To Array mdadm --manage /dev/md0 --add /dev/sda