raid_recovery

# clear MBR
dd if=/dev/sdOld of=/dev/sdNew bs=512 count=1

# replicate sdOld partition table
sfdisk -d /dev/sdOld | sfdisk /dev/sdNew

# add new disk to RAID
mdadm --manage /dev/md12X --add /dev/sdNewX

mount /dev/centos/root /mnt/custom
for i in /dev /dev/pts /proc /sys /run; do mount -B $i /mnt/custom$i; done
chroot /mnt/custom /bin/bash

# reinstall kernel
yum reinstall kernel

grub2-install /dev/sda
grub2-install /dev/sdb
grub2-mkconfig -o /boot/grub2/grub.cfg