convert ext4 to btrfs

readme.md

convert a partition from ext4 to btrfs

Sources (March 2025):

• https://www.youtube.com/watch?v=o-3_ZlvsZAI (grub for ext4 @ ~1h24)
• https://btrfs.readthedocs.io/en/latest/Compression.html
• https://btrfs.readthedocs.io/en/latest/btrfs-device.html
• https://www.lorenzobettini.it/2022/10/timeshift-and-grub-btrfs-in-ubuntu/

Important

these steps worked for me! your milage may vary!
remember that these steps could lead to an UNBOOTABLE system or to DATALOSS.
take nessesary precaution and backups!

boot into a live envirionment

• create a backup of the disc with dd
• convert the ext4 volume into a new btrfs volume

sudo btrfs-convert <DISK>

• mount the new volume and navigate into it.

sudo mount -o subvol=@ /dev/sdxY /mnt

• create a new btrfs sub volume

sudo btrfs subvol create @

Important

For Timeshift to work the root subvolume must be named @.
(optional) More Subvolumes can be created like @home, @cache and so on.

• move / into the new subvolume.
  • (the error, that @ cannot be moved into itself can be ignored)

sudo mv * @/

chroot into the new btrfs partition

mount the root partition

sudo mount -o subvol=@ /dev/sdxY /mnt

mount the boot partition

sudo mount /dev/sdzY /mnt/boot

mount the efi partition (UEFI Boot)

sudo mount /dev/sdwY /mnt/boot/efi

mount system

for dir in /dev /dev/pts /proc /sys /run; do sudo mount --bind $dir /mnt$dir; done

chroot into the installation

sudo chroot /mnt /bin/bash

change /etc/fstab

• set UUID of the new disc
• type von ext4 zu btrfs ändern.
• set these options:
  • defaults,noatime,space_cache=v2,compress=zstd:3,subvol=@
• defrag the btrfs filesystem and compress it:

sudo btrfs fi defragment / -r -czstd

Important

the root partition is now compressed. To mount it in the future use:

sudo mount -o subvol=@ -o compress=zstd /dev/sdxY /mnt

update grub

when chroot'ed into the system it should be enough to just update the grub config:

sudo grub-mkconfig -o /boot/grub/grub.cfg
sudo update-grub

otherwise try:

edit the file `/boot/efi/EFI/ubuntu/grub.cfg

• set the new UUID of the Root-Partition
• update the path with the prefix /@

update the grub launcher directly:

• File location: /boot/grub/grub.cfg
• search for submenu
  • old value: /boot/vmlinuz...
  • new value: /@/boot/vmlinuz...
  • update the UUID
  • add rootflags=subvol=@ after ro

update initramfs

• if a swap-partition and the file /etc/initramfs-tools/conf.d/resume exists, update the UUID inside this file.
• install btrfs-progs if not already present: sudo apt install btrfs-progs
• finally sudo update-initramfs -u

now reboot