BTRFS is one of the contenders for the successor to EXT4, which has already been around for a few years. Today I will show you how to configure BTRFS on a Raspberry Pi 64 bit system in the kernel and how to create an automated backup solution with btrbk.

Create a complete backup of your Raspberry Pi, e.g. with dd. There is always something that can go wrong.These instructions refer to kernel version 6.1.21-v8. You can check your kernel version with the command uname -a.

check kernel version

Debian 12 bookworm was used as the OS. You can see your OS version under /etc/os-release:

/etc/os-release/etc/os-release

There should be enough free space on your Raspberry Pi file system. As a rule of thumb, about 50 percent. However, the convert process can also be successful with much less. In my case, for example, less than 10 percent disk space was still free.

If not already available, install intiramfs-tools, btrfs and btrbk:

Add the btrfs module via initramfs modules in /etc/initramfs-tools/modules by simply adding btrfs at the end of the file:

/etc/initramfs-tools/modules

If you run the mkinitramfs command you get strange errors like "Missing /boot/config-[kernel_version]" and that zstd or gzip is not supported by the current kernel.mkinitramfs has not yet (as of January 2024) been configured for the RaspberryPi 64Bit, so we have to make a change in the setup file.

In /usr/sbin/mkinitramfs add the following lines below the existing shebang #!/bin/sh:

/usr/sbin/mkinitramfs/usr/sbin/mkinitramfs

and create a new initramfs:

Beware: From here, your Raspberry Pi will be switched to BTRFS after restarting. Without changing the file system afterwards, your Raspberry Pi will no longer start.

Now change to directory /boot/ and replace ext4 with btrfs in /boot/cmdline.txt manually with any editor such as nano or vim.

Load the new kernel configuration at each boot with the following entry at the end of the configuration in /boot/config.txt:

/boot/config.txt

The last change is made in the /etc/fstab. Change the file system for the root partition (not for boot) to btrfs manually with any editor such as vim.

/etc/fstab

Now shutdown your Raspberry Pi remove your flash drive and plug it into a separate system.

Your flash drive must not be mounted and btrfs-progs must be installed on your system.Check for your drive with lsblk.

flash drive filesystem

By default, your Raspberry Pi uses two partitions. We want to convert rootfs. bootfs remains untouched. Check carefully if this is really the right partition you want to convert to btrfs. In the example, sdd2 is the correct partition. That doesn't have to be the case for you.

First check the partition for possible errors. This step is not absolutely necessary.

Then you can use the btrfs-convert function.

This process can take a very long time. It is a process consisting of three steps:

The critical process is the first, because it could fail due to insufficient disk space.As soon as the process is complete, you will receive the message 'conversion complete'.

If you convert your file system using btrfs-convert, you create a BTRFS filesystem with a two subvolume for ext2_saved and another for rootfs without UUID. It is not possible to create snapshots of subvolumes without UUIDs with btrbk.

Mount your devices locally again and check if everything is ok (it should be).

Go to your mountpoint /mnt and create a new subvolume for your root device.

Btrfs subvolumes behave like normal directories in Linux. All operations such as rm or ls also work here. We use this fact to migrate the data from root to the new subvolume. By naming convention, subvolumes are preceded by an @ character.

Check if the subvolume creation has worked:

We now need to move the files from / to the new subvolume. Many tutorials on the Internet specify a rsync command for reasons I don't understand. However, a pure mv command is sufficient and much faster.

This command will move all directories on your mounted drive to @root subvolume except @root itself.:

Migrate root filesystem to btrfs subvolume @root

This will take a very long time, depending on storage consumption but is still faster than rsync.

Reconnect your flash drive to your raspberry pi and let it boot up.

Test if everything is ok and delete the subvolume ext2_saved since it takes up a lot of space:

delete ext2_saved

As you can see, there is no snapshot yet. Create the first snapshot with the command:

This creates a snapshot in the /snaphosts directory which hardly takes up any disk space.

If you are using a swap file, you will need to make additional changes. The steps are described very well in the official documentation but despite these measures it is not possible to create snapshots without first deactivating the swap. You get the error message:

Theoretically, this could be avoided by creating a separate subvolume for the swap file.Another way is to use zram as an alternative to swapfile. zram allocates swap in RAM. A small positive side effect is the performance gain.

The configuration is simple.

Comment out the line PERCENT=50 in the file /etc/default/zramswap and enable the service:

Create a new file /etc/btrbk/btrbk.conf and add the following to it:

/etc/btrbk/btrbk.conf

We now need a snapshot directory. In the configuration above I called this SNAPSHOT. btrbk does not create this directory, so we have to do that:

Now we can test the configuration:

A successful test should show the following:

The /etc/btrbk directory also contains a more detailed example configuration.It is also possible, for example, to perform both pull and push backups remotely with btrbk via SSH.The file is called btrbk.conf.example and is well commented.The current configuration will create 7 backups with a daily time span.

However, we also need to trigger the backup process. To do this, we create a SystemD unit configuration file in /etc/systemd/system

btrbk-local-snapshot.service

btrbk-local-snapshot.timer

In the example, a snapshot is taken every night at 23:55.

As long as BTRFS is not in the kernel by default, you will have to make the adjustments to initramfs again with every kernel update (mkinitramfs step). However, this will become faster and faster over time.