Quota for Home Directories in Linux using BTRFS

I have a big drive on a home linux server and I want to give a small slice of it to some friends. With multiple people doing the same, we get a simple storage network for cheap offsite backups.

The server is a Raspberry Pi, the drive is a 4TB WD USB disk.

Requirements

A large BTRFS formatted volume, mounted on /mnt/big
Logged in as root, cd /mnt/big
I want to create a new user, “foo”, with homedirectory /home/foo stored on the big drive, with an artificial disk quota of 1TB.

Steps

Enable quota on the disk:

btrfs quota enable .

Create a subvolume:

btrfs subvolume create foo

You have a directory “foo” that is also a subvolume. Set its quota:

btrfs qgroup limit 1T foo

Create the new user:

useradd -m foo
chown foo:foo /mnt/big/foo
chmod 700 /mnt/big/foo

Bonus: move all skeleton created files from the new home directory to the subvolume:

find /home/foo -mindepth 1 -maxdepth 1 -exec mv {} ./foo/ ";"

There are probably better ways to do that but this worked for me.

I make the unmounted home directory inaccessible to the new user so it fails loudly when I forget to mount the btrfs subvolume (e.g. after restart):

sudo chown root:root /home/foo

These permissions will get reset to foo:foo automatically on mount

Make sure your btrfs drive has a label:

btrfs filesystem label .

If that doesn’t return anything, set one:

btrfs filesystem label . my_btrfs_drive

Now mount the subvolume as the user’s homedir by adding this to /etc/fstab:

LABEL=my_btrfs_drive     /home/foo      btrfs   subvol=/foo,noatime     0   0

And mount everything:

mount -a

Done! You now have a user “foo” with a home directory mounted from a btrfs subvolume, with a quota of 1TB on their subvolume (i.e. home directory). You can take snapshots of this subvolume at will.

To see disk usage of all subvolumes of your entire btrfs drive:

btrfs qgroup show .

qgroupid         rfer         excl
--------         ----         ----
0/5         757.68GiB    224.48GiB
0/1013          0.00B        0.00B
0/1017      607.32GiB     74.11GiB
0/1018       20.00KiB     20.00KiB

The rfer column is total disk size, the excl column is for data that is unique to that volume.

To see quota usage for a subvolume:

btrfs qgroup show -reF foo

qgroupid         rfer         excl     max_rfer     max_excl
--------         ----         ----     --------     --------
0/1017      607.32GiB     74.11GiB      2.00TiB         none

Same as above, but it tells you exactly what the limits are.

Requirements

Steps

Sources