BTRFS on Alpine Linux

Dec 31 2021

I'm currently in the midst of migrating some of my infrastructure from the cloud to "on prem", aka a local server, aka my old PC. I wanted to try alpine linux as the host OS to see how it behaves as a lightweight server distro.

So far it stands up quite nicely, it has everything you'd expect from a linux-based operating system. The only problem I encountered was getting BTRFS to work out of the box. Here are some things you should know when using BTRFS on Alpine linux.

Installing BTRFS

Installing BTRFS is relatively straight forward. Simply install the package and tell Alpine to load the module on startup:

apk add btrfs-progs
echo btrfs >> /etc/modules

To load the module right away, you can use the following command:

modprobe btrfs

Mounting a volume

If you try mounting a btrfs volume via your fstab, you will get an error. This is because BTRFS does not know about the drives yet when the filesystems are mounted. To work around this, you can create an OpenRC service that runs a btrfs scan to detect the drives. To do so, create a service under /etc/init.d/btrfs-scan with the following content:

#!/sbin/openrc-run

name="btrfs-scan"

depend() {
  before localmount
}

start() {
  /sbin/btrfs device scan
}

Make the service executable and register it:

chmod +x /etc/init.d/btrfs-scan
rc-update add btrfs-scan boot

Now, you should be able to add the volume to your /etc/fstab:

UUID=abcdef-0055-4958-990f-1413ed1186ec  /var/data  btrfs   defaults,nofail,subvol=@  0  0

After a reboot, you should be able to see the drive mounted at /var/data.

Resources

This is post 023 of #100DaysToOffload.


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