BTRFS Guide - Basic Commands, Snapshots, and RAID

Jan 13, 2020 | Linux

This guide goes over everything you need to know to get started on BTRFS. With that said we will be going over the basic structure of BTRFS and the things you should and should not do.

Creating a BTRFS Filesystem

Create the file system on an empty btrfs partition

mkfs.btrfs /dev/sda1
Note: You will need to mount this file system after

Now we need to make a subvolume before we add data to the device

btrfs subvolume create /mnt/sda1 /mnt/sda1 is the mount point!

After this is complete you can now write data to your BTRFS volume and use all it capabilities.

Basic BTRFS Layout
Note: Top Level 5 is root and isn’t a btrfs subvolume that can do snapshots and other btrfs features and therefore should not be mounted

toplevel root level 5
  +-- root\@ level 256 (subvolume root mounted at / id varies)
  +-- root\.snapshots level 256 (typical snapshot subvolume)

Basic Commands

  • Disk free
    sudo btrfs fi show

Output:
File System Output

  • Disk Usage
    sudo btrfs fi du / Note: you can make / any other mount point
  • Scrub SubVolume Recommended running every week!
    sudo btrfs scrub start /
  • Balance Subvolume for Performance
    sudo btrfs balance start -musage=50 -dusage=50 /
    Note: Use the musgae and dusage filters to only balance used blocks above 50 percent utilization
    sudo btrfs balance cancel / Stops running balance
  • List Subvolumes based on mountpoint
    sudo btrfs subv list /home

Output:
Subvolume Output

  • Mount Subvolume
    sudo mount -o subvolid=267 /dev/sda1 /media/games
    OR add this to /etc/fstab
    UUID=IDGOESHERE /media/games rw,exec,subvolid=267 0 0

Snapshots

Snapshots are one of the best things about BTRFS and I absolutely love them. They are incredible powerful and beneficial.

So Lets run through some scenarios when you use Snapshots.

Create Snapshot

sudo btrfs subv snapshot /home /home/.snapshots/2020-01-13

Using this you can revert the snapshot by simply editing the /etc/fstab and changing the subvol=2020-01-13 or the corresponding subvolid you get from sudo btrfs subv list /home

Restore Snapshot

Restore Snapshot after reboot and successful rollback

sudo btrfs subv delete /home
sudo btrfs subv snapshot /home/.snapshots/2020-01-13 /home

Now simply restore your fstab and reboot to be back on the /home subvolume.

The reason to do it using this method is to verify the data first. If it doesn’t work out you can simply change the /etc/fstab back and you will be back to where you started.

Multiple disks and RAID

Oh boy, here we go. This is such a badly misunderstood subject and if you aren’t careful you will be causing more problems than you are looking to solve. So with that let’s get into RAID. I will NOT be cover RAID 5 as it is unstable and SHOULD NOT BE USED!

Must know commands for multiple disks:

Add Disks before creating subvolume: sudo btrfs device add /dev/sda1 /dev/sdb1
Add Disk to existing subvolume: sudo btrfs device add /dev/sdb1 /home
Delete Disk from subvolume: sudo btrfs device delete /dev/sdb1 /home

Creating the RAID File System:

RAID 1: sudo btrfs -m raid1 -d raid1 /dev/sda1 /dev/sdb1
RAID 10: sudo btrfs -m raid10 -d raid10 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1

Convert to to RAID 1 after adding disk to existing subvolume

btrfs balance start -mconvert=raid1 -dconvert=raid1 /home

I could put RAID 0 here… but honestly you should just use EXT4 or XFS if you are looking for performance. It would be better than using BTRFS!

Video Walkthrough

#BTRFS