Scan and assemble:
# mdadm --assemble --scan
Scan to update mdadm.conf
# mdadm -Es >> /etc/mdadm/mdadm.conf
If not md device has been found, or you have only one disk from two of the RAID1, you can force to re-create the md device. The important parameter is “missing”, that will make mdadm to create the mirror with only one member:
# mdadm --create /dev/md127 --assume-clean --level=mirror --verbose --raid-devices=2 /dev/sda missing mdadm: /dev/sda appears to be part of a raid array: level=raid1 devices=2 ctime=Sat Jan 21 06:33:20 2017 mdadm: Note: this array has metadata at the start and may not be suitable as a boot device. If you plan to store '/boot' on this device please ensure that your boot-loader understands md/v1.x metadata, or use --metadata=0.90 mdadm: size set to 1464991744K mdadm: automatically enabling write-intent bitmap on large array Continue creating array? y mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md127 started.