Date: 2021jan23 OS: Linux Distro: Fedora Q. Fedora: enable btrfs compression A. This worked for me on a VM. (I had a couple missteps which I'll omit for your benefit) - Installed Fedora 33 on a fresh VM, btrfs is the default for / and /home. While ext4 is used for /boot But compression is not enabled. - At one point I messed up and tried to reboot in single user mode but was denied with "Root account is locked" so had to delete the entire VM and try again. So next time I unlocked root with `sudo passwd root`. If your system is on the internet, you add can `PermitRootLogin no` to /etc/ssh/sshd_config for safety - Add the compress option to /etc/fstab Before

UUID=nnn / btrfs subvol=root 0 0 UUID=nnn /boot ext4 defaults 1 2 UUID=nnn /home btrfs subvol=home 0 0

With the option

UUID=nnn / btrfs subvol=root,compress 0 0 UUID=nnn /boot ext4 defaults 1 2 UUID=nnn /home btrfs subvol=home,compress 0 0

- Remount

mount -o remount /home mount -o remount /

That will only compress new files. - To compress existing files do

btrfs filesystem defragment -r /home btrfs filesystem defragment -r /

This only took a few seconds on my new system but may take a while for a full filesystem. - Look at how it went

dnf install compsize compsize /home compsize /

This will show you how well the compress when and the type of compression being used. It was zlib for me. Example output

Processed 140058 files, 133128 regular extents (196786 refs), 80886 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 93% 14G 15G 12G none 100% 13G 13G 10G zlib 41% 628M 1.4G 1.4G zstd 28% 42M 148M 148M

From https://github.com/kilobyte/compsize - That's it! - Optionally you can specify the type of compression in /etc/fstab using compress=zlib compress=zstd compress=lzo compress=no