====== BTRFS snapshot size ======
* First you need to enable quota
sudo btrfs quota enable /home
* You need to wait for BTRFS so scan the filesystem for quota usage, then
sudo btrfs qgroup show /home
* You get output which looks like this:
qgroupid rfer excl
-------- ---- ----
0/5 142.21GiB 89.70MiB
0/410 96.00KiB 96.00KiB
0/2191 17.62GiB 0.00B
0/3237 137.90GiB 4.05GiB
''qgroupid'' is the snapshot ID, ''rfer'' is the total size of that snapshot (the size of the parent subvolumes are included), ''excl'' is the exclusive space that particular snapshot occupies.
===== Deleting snapshots =====
* You can list all the subvolume by running this:
sudo btrfs subvolume list /home
Note that this will display the link between the ''BTRFS_SNAPSHOT_ID'' and ''SNAPPER_SNAPSHOT_ID''.
* Note that if you are using snapper, you should delete snapshots using:
snapper -c home delete $SNAPPER_ID
You shouldn't delete the snapshot using ''btrfs subvolume delete'', as this will confuse Snapper.
===== Re-initialise qgroups =====
If your filesystem has just suffered an episode of catastrophic failure, you might need to re-initialise things. A Snapper rollback can cause it.
for i in $(btrfs qgroup show /home | tail -n+3 | cut -d ' ' -f 1); do btrfs qgroup destroy $i /home; done
btrfs quota disable /home
btrfs quota enable /home