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Last active July 21, 2024 00:57
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Resources for BTRFS Setup and Management
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btrfs.md

BTRFS Notes

Packages

  • btrfs-progs
  • duperemove

Suggested BTRFS subvol as / layout for Snapper

https://wiki.archlinux.org/title/Snapper#Suggested_filesystem_layout

This allows for rolling the rootfs back to a snapshotted version, since the rootfs isn't tied to vol-id 5, anymore.

Debian installer uses /@rootfs as the subvol /, instead of @. See https://wiki.debian.org/Btrfs%20migration for more information.

When you need to make /@ level changes, you will still need to mount subvol-id 5 in /mnt.

sudo mount /dev/nvme0n1p3 /mnt

Resources

Modifications

  • Label the main/root btrfs filesystem root-btrfs and the boot filesystem boot-btrfs.
sudo chattr +C  /var/lib/libvirt/images
sudo chattr +C ~/.local/share/libvirt/images
sudo chattr +C ~/.local/share/gnome-boxes/images

Swap

sudo mount /dev/disk/by-label/root-btrfs -osubvolid=5 /mnt
sudo btrfs subvolume create /mnt/@swap
sudo chmod u=rwx,g=,o= /mnt/@swap
sudo umount /mnt
sudo mkdir /var/swap
sudo chmod u=rwx,g=,o= /var/swap

# Edit /etc/fstab to mount @swap to /var/swap.
sudo systemctl daemon-reload
sudo mount /var/swap

sudo btrfs -v filesystem mkswapfile -s 8g /var/swap/swapfile1
sudo ls -al /var/swap

# Edit /etc/fstab and add the following line:
# /var/swap/swapfile1 none swap defaults 0 0
sudo swapon -a
sudo swapon

# Example mount line for the swap subvol:
# sudo mount /dev/disk/by-label/root-btrfs -osubvol=@swap /var/swap

Add Mirrored Drive

sudo btrfs device add -f /dev/mapper/root2_crypt /
sudo btrfs balance start -dconvert=raid1 -mconvert=raid1 /

Maintenance

sudo btrfs scrub start /
sudo btrfs scrub status /
sudo btrfs filesystem defragment -r /

sudo duperemove -rdh /
# Or, you can speed things up with a hashfile, which will then
# use the save hash if the timestamp matches.
sudo duperemove  -rdh -A --hashfile=/duperemove_hashfile /

The -A allow it to work over readonly snapshots.

Warning: Running duperemove cannot effectively remege/resnapshot two unrelated subvolumes/snapshots. I did the following experiment, to test this. Restore root and home from a backup, manually using rsync. I then used btrfs send/receive to send the same backup as a subvolume to the machine being restored. I ran duperemove many times, but the most storage space I could recover/merge was about 200GB of 800GB. I still had a massive 600GB of undedupeable additional storage being consumed by this subvol that contains identical data to my main subvols.

Interesting BTRFS Related Packages

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