1. reassemble way

mdadm --stop /dev/md0

mdadm --assemble /dev/md0 /dev/sd[cd]1

mdadm --detail /dev/md0

mdadm --detail --scan --verbose > /etc/mdadm.conf

[NOTICE] add DEVICE

vi /etc/mdadm.conf

ARRAY /dev/md0 level=raid1 num-devices=2 metadata=1.2 name=owl49:0 UUID=xxxxxxxx:0e451cef:a240f6e8:bf4734b4

devices=/dev/sdb1,/dev/sdc1

DEVICE /dev/sdb1

DEVICE /dev/sdc1

2. make it fail manually & remove & add

# check example
mdadm --examine /dev/sd[a-z]

# check disks
fdisk -l

# make fail for test
mdadm /dev/md0 -f /dev/sdb1

# remove the disk failed
mdadm /dev/md0 --remove /dev/sdb1

# add new disk
mdadm /dev/md0 --add /dev/sdb1

# check stat
cat /proc/mdstat