btrfs_ext_disk_backup

I've created this script to mirror local btrfs snapshots via btrbk to an external disk (for e.g. USB device).

preface

This is more like a template and documentation for myself. It's not a complete solution for your backup, bu can be a part of it! You should definitely have some kind of automatic backup!

setup

In this example the external disk is /dev/sdb. Please check with lsblk and dmesg yourself if you're using the correct device. Please be aware that you will delete all data on the external device if you follow the steps in this tutorial.

1. create a partition on your external disk, for e.g. via parted:

   parted /dev/sdb
   print free
   mklabel GPT
   mkpart primary 0% 100%
   quit
   

2. Encrypt the disk via LUKS:

   sudo cryptsetup luksFormat /dev/sdb1
   

3. Create a Keyfile for LUKS

   sudo dd if=/dev/urandom of=/crypto_keyfile.bin bs=1024 count=4
   

4. update permissions for the keyfile:

   sudo chmod 400 /crypto_keyfile.bin
   

5. add the keyfile to the LUKS device:

   sudo cryptsetup luksAddKey /dev/sdX /root/keyfile 
   

6. Open the LUKS device and format it with btrfs

   sudo cryptsetup luksOpen /dev/sdb1 backup_disk
   sudo mkfs.btrfs /dev/mapper/backup_disk
   sudo cryptsetup luksClose backup_disk
   

7. The btrbk.conf assumes that you have mounted your local btrfs partition with all suvolumes in /mnt/btr_pool and have a subvolume @snapshots in it. I backup my @ and @home subvolumes, you may need to change this in the btrbk.conf. The dir should look like this:

   $ ls /mnt/btr_pool/
   @  @cache  @home  @snapshots  timeshift-btrfs
   

   The entry in /etc/fstab could look like this:

   # /dev/mapper/manjaro-root all subvolumes for btrbk
   UUID=78fa5e8c-dc17-4f58-bada-00c1f3e935f3	/mnt/btr_pool         	btrfs     	rw,noatime,compress=zstd:3,ssd,space_cache,commit=120	0 0
   

8. now you need to add the btrbk_external_disk.vars file. You can copy the btrbk_external_disk.vars.example file.

   • To get the BACKUP_DISK_UUID use lsblk -f which will show your blockdevices with their corresponding UUIDs. You need the UUID from the LUKS device, not the mounted LUKS device which holds the btrfs volume.
   • Check if you need the path to your keyfile and update LUKS_KEYFILE.

9. If the devices and the path is present you should be able to run bash run_btrbk_external_disk.sh

running your backup

I regularly attach my USB disk to my notebook and run the script manually. It's possible to create a udev rule for it to automate the process. You need to set the path to the file containing the variables via the first argument of the shellscript, for e.g.: bash run_btrbk_external_disk.sh /home/foo/backup/btrbk_external_disk.vars.

Please be aware that you should always check if the backup runs as expected. You could add a email output or use notify-send.

restore / restore test

Please refer to the README of btrbk. You should test you backups from time to time.