Migrate USB OS to mdadm RAID array on Arch Linux

gistfile1.sh

# Create new array
mdadm --zero-superblock /dev/sd{a,b}
mdadm -C --level 1 /dev/md1 -n 2 /dev/sda2 /dev/sdb2

# Save to mdadm.conf since it will be used in initramfs for assembling arrays
mdadm --detail --scan >> /etc/mdadm.conf

# Make new file system and then migrate data
rsync -avxHAXS -P / /mnt/md1

# Chroot into the new world
cd /mnt/md1
mount -t proc proc proc/
mount --rbind /sys sys/
mount --rbind /dev dev/
mount --rbind /run run/
chroot /mnt/md1 /bin/bash

# Rebuild initramfs
# Add mdadm_udev to the HOOKS section of the mkinitcpio.conf first, then:
mkinitcpio -p linux
# Add MODULES="xfs" and BINARIES="fsck.xfs" to /etc/mkinitcpio.conf if needed

# (Chroot-ed) Edit /etc/fstab according to new `blkid` and then:
grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/sda
grub-install /dev/sdb

# Verify success
reboot

# Ref(outdated): https://wiki.archlinux.org/index.php/Convert_a_single_drive_system_to_RAID