howto-qubes-btrfs-convert.md

EXPERIMENTAL: Convert a Qubes R4.0 installation from file on ext4 to file-reflink on btrfs

0. Ensure that you have a working backup of all VMs.

1. Find the UUID of the LUKS device hosting the dom0 ext4 root filesystem:

   grep -Eo '^/dev/mapper/luks-[0-9a-f-]{36} / ext4 ' /proc/mounts | cut -b 18-54
   

   Write down the output on a piece of paper.

2. For those dom0 kernels with btrfs support built as a module, include it in their initrds:

   sudo dracut --regenerate-all --force --add-drivers btrfs
   

3. Reboot into a Qubes R4.1 installer (not R4.0, which has a severely broken btrfs-convert version!), and switch to a console.

4. Decrypt the ext4 root filesystem:

   cryptsetup open /dev/disk/by-uuid/YOUR-LUKS-UUID-FROM-STEP-ONE rootfs
   

5. Convert the decrypted filesystem to btrfs, and restore its old filesystem UUID:

   FSUUID=$(blkid -s UUID -o value /dev/mapper/rootfs)
   echo $FSUUID
   
   e2fsck -f     /dev/mapper/rootfs
   btrfs-convert /dev/mapper/rootfs
   btrfs check   /dev/mapper/rootfs
   
   btrfstune -U $FSUUID /dev/mapper/rootfs
   

6. Switch the varlibqubes pool driver from file to file-reflink:

   mkdir /mnt/rootfs
   mount /dev/mapper/rootfs /mnt/rootfs
   
   sed '/ name="varlibqubes"/s/ driver="file"/ driver="file-reflink"/' -i.bak /mnt/rootfs/var/lib/qubes/qubes.xml
   diff -u /mnt/rootfs/var/lib/qubes/qubes.xml{.bak,}
   
   umount /mnt/rootfs
   

7. Reboot into Qubes

8. Check that the varlibqubes pool has been switched to file-reflink:

   qvm-pool
   

9. Everything's working? Then clean up the remaining file/ext4 cruft:

   sudo rm -f /var/lib/qubes/*/*/*-cow.img*
   sudo btrfs subvolume delete /ext2_saved