The backup/restore procedure involves only a few steps:

Full backup

rsync -av --delete \
    /etc /var /home /bin /boot /lib /lib64 /opt /root /sbin /run /tmp /usr \
    --exclude /run/media --exclude /var/lib/docker --exclude /var/lib/mongodb/journal \
    /run/media/…/save_path/

Booting from an USB key

• download the latest ISO
• Follow the installation guide to:
  • check the image checksum / signature
  • dd it onto the USB key
  • boot on it

Restoring and preparing the reboot

• partition (cfdisk) / format (mkfs.ext4 -m 0 -r 0 / mkswap) / mount you storage drive once booted.
• restore the backup with rsync again.
• Check your new root/swap UUIDs with blkid and replace them in ${TARGET}/etc/fstab.
• chroot into target and run grub-mkconfig -o /boot/grub/grub.cfg to update the GRUB configuration.

Reboot, and you’re done.

I still can’t handle how Arch is SIMPLE. Not easy. SIMPLE. Wow. Thanks.