My personal notes on the Btrfs file system

Last updated: Oct 20, 2024

Btrfs is a relatively new file system which offers a number of features such as transparent compression, snapshots, online volume resizing, etc… It is increasingly used in GNU/Linux distributions. Here, I'll outline the main commands you need to know when using this file system.

Extend Partition Size

⚠️To avoid data loss, ensure to back up your data before starting any resizing task. And make sure you understand the commands before entering them.⚠️

Let's assume we have this type of disk configuration:

First, we need to reconfigure the disk boundaries:

root@host:~# gdisk /dev/sda

Command (? for help): d
Partition number (1-3): 3

Command (? for help): n
Partition number (3-128, default 3): 3
First sector (34-125829086, default = 3147776) or {+-}size{KMGTP}: 3147776
Last sector (3147776-125829086, default = 167772126) or {+-}size{KMGTP}: 
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): 
Changed type of partition to 'Linux filesystem'

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/sda.
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.

root@host:~# partprobe

Extend the file system size to the maximum size available on the partition:

root@host:~# btrfs filesystem resize max /

We can also reduce or extend the file system to a specific size:

root@host:~# btrfs filesystem resize -1G /data/

Commands

Scrub

Performs an online file system check:

root@host:~# btrfs scrub start /

Check status of running scrub:

root@host:~# btrfs scrub status /

Subvolumes

Subvolumes provide:
- Isolation: Subvolumes can be used to isolate different parts of your file system
- Snapshots: Subvolumes can be independently snapshotted
- Separate mount point: Subvolumes can be mounted independently at different points in the file system hierarchy.
- Quotas: Btrfs lets you set quotas on subvolumes

Graphical view of Btrfs subvolumes:

Disk partition scheme showing Btrfs subvolumes

Create a subvolume:

root@host:~# btrfs subvolume create /home/SUBV

List subvolumes:

root@host:~# btrfs subvolume list /

Mount subvolume:

root@host:~# mount /dev/sda3 -o subvol=SUBV /home/SUBV/

Misc

Format partition with Btrfs file system:

root@host:~# mkfs.btrfs /dev/sdb1

Start an online degragmentation:

root@host:~# btrfs filesystem defragment -r -v /

Show detailed information about internal filesystem usage:

root@host:~# btrfs filesystem usage /

Summarize disk usage of each file:

root@host:~# btrfs filesystem du /home/user/file

Show space usage information for a mount point:

root@host:~# btrfs filesystem df /

Show device IO error statistics:

root@host:~# btrfs dev stats /

Show disk infos (uuid, occuped space etc…):

root@host:~# btrfs filesystem show /

Snaphots

List subvolumes and snapshots in the root node:

root@host:~# btrfs subvolume list /

Create a snapshot of the root directory:

root@host:~# mkdir /.snapshots root@host:~# btrfs subvolume snapshot -r / /.snapshots/\@$(date +%Y.%m.%d)

Deleting a snapshot:

root@host:~# btrfs subvolume delete /.snapshots/@2024.05.04/

Compression

Modify the /etc/fstab file so that each new file is automatically taken into account for compression:

UUID=4e39e49c-6934-41f5-97fd-cb7c699a78a5 / btrfs defaults,compress=zstd,subvol=@rootfs 0 0

Compressing files in a specific folder:

root@host:~# btrfs filesystem defragment -r -v -czstd /home/user/

Computing

Music

Misc

My personal notes on the Btrfs file system

Extend Partition Size

Commands

Scrub

Subvolumes

Misc

Snaphots

Compression

References