btrfs

filesystem

btrfs filesystem usage "/"

btrfs filesystem df "/"

btrfs filesystem show "/"

# assign label to a btrfs filesystem
btrfs filesystem label /dev/mapper/lala LALA

subvolume

• Subvolumes within a btrfs filesystem share the same UUID (same device!)
• That means that subvolumes share the same maximum device size
• The same device (with different subvolumes) is mounted into different mount points
• There is a convention to use prefix the subvolume name with @ to indicate that it will be used as mount point. And @ to the subvolume that will be mounted to root
• The top level subvolume is ID=5, subvol=/
• A size quota can be imposed for each subvolume
• Subvolumes can be referenced in fstab by name (e.g., subvol=/@files ) or by id (e.g., subvolid=243) mount flags

# List all subvolumes and snapshots in the filesystem
btrfs subvolume list "/"

# Create subvolume
btrfs subvolume create "/new-subvol"
mount "/dev/sda" "/home" -o subvol=/path/to/subvolume,subvolid=objectid

# take a snapshot of a subvolume (the snapshot itself is created as a new subvolume)
btrfs subvolume snapshot "/" "/my-snapshot"

# default subvolume
btrfs subvolume get-default "."

# set the default volume (to be mounted without specifying subvol or subvolid)
btrfs subvolume set-default "/mnt"

rescue

# Clear the tree log. Usable if it's corrupted and prevents mount
btrfs rescue zero-log "/dev/mapper/a"