Btrfs

Links

• Wiki: https://btrfs.wiki.kernel.org/index.php/Main_Page
  • Getting started
  • FAQ
  • UseCases / Recipes
  • Sysadmin Guide
  • Multiple Devices
  • Problem FAQ
  • Gotchas
  • Incremental Backup
• Read the Docs: https://btrfs.readthedocs.io/
  • man pages: https://btrfs.readthedocs.io/en/latest/man-index.html
  • mount options: https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#mount-options
• Btrfs @ Arch Linux: https://wiki.archlinux.org/title/btrfs
• Videos and Talks
  • Linuxcon Japan 2014 - Btrfs Talk
    • YouTube: https://www.youtube.com/watch?v=ND3OKCP70_I
    • Slides: http://marc.merlins.org/linux/talks/Btrfs-LC2014-JP/Btrfs.pdf
  • Btrfs is awesome except when it isn’t (2019) - many good disaster recovery hints: https://www.youtube.com/watch?v=qHalOdCZO9Q
  • btrfs: The Best Filesystem You’ve Never Heard Of (2017): https://www.youtube.com/watch?v=-m01x3gHNjg
  • TUT91782 Getting the most out of the btrfs filesystem (2017) - tech internals: https://www.youtube.com/watch?v=iwNg_fusT9A

Tasks

• check free space: btrfs filesystem usage <path>
• allocation of block group types: btrfs filesystem df <path> (supports --format json)
• device stats (io errors): btrfs device stats <path> (supports --format json)
• show subvolumes: btrfs sub list <path>

Check redundancy (after a replaced disk)

• use btrfs filesystem usage -T <path> to check if all data, metadata and system is not “single” stored
• fix this with btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft /mnt/btrfs
• see https://wiki.tnonline.net/w/Btrfs/Replacing_a_disk

Commands

balance

• see https://btrfs.readthedocs.io/en/latest/btrfs-balance.html
• filters
  • soft: when converting between profiles chunks that already have the target profile are left untouched

replace

• see https://btrfs.readthedocs.io/en/latest/btrfs-replace.html
• start subcommand with -r: only read from srcdev if no other zero-defect mirror exists. (enable this if your drive has lots of read errors, the access would be very slow)

Other Commands

# create raid1
mkfs.btrfs -m raid1 -d raid1 /dev/sda1 /dev/sdb1

# mount
mkdir /mnt/btrfs
mount -o compress=zstd /dev/sda1 /mnt/btrfs

# scrub
btrfs scrub start /mnt/btrfs
btrfs scrub status /mnt/btrfs

# show filesystem
btrfs filesystem show

# pull one drive and scrub + show

# replace disk 1
btrfs replace start 1 /dev/sdc1 /mnt/btrfs -f
btrfs replace status /mnt/btrfs

# device stats
btrfs device stats /mnt/btrfs