How properly remove a Btrfs pool and free up space in the system?

Hello There,

I wanted to delete a 150G Btrfs pool from my lxd server:

$ lxc storage show costorage1
  size: 150GB
  source: /var/snap/lxd/common/lxd/disks/costorage1.img
description: ""
name: costorage1
driver: btrfs
- /1.0/profiles/default
status: Created
- none

And resize it to 50G or delete it and create a new pool with 50G.

I tried:

lxc profile device remove costorage1 root

However, that did not help to accomplish freeing the space from the system.

I still see the 212G of space used on my system:

    $ df -h
        Filesystem      Size  Used Avail Use% Mounted on
        udev            7.8G     0  7.8G   0% /dev
        tmpfs           1.6G  2.1M  1.6G   1% /run
        /dev/sda2       234G  212G  9.8G  96% /
        tmpfs           7.8G   67M  7.8G   1% /dev/shm
        tmpfs           5.0M  4.0K  5.0M   1% /run/lock
        tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
        /dev/loop1      9.2M  9.2M     0 100% /snap/canonical-livepatch/95
        /dev/loop2      162M  162M     0 100% /snap/gnome-3-28-1804/128
        /dev/loop3      256M  256M     0 100% /snap/gnome-3-34-1804/36
        /dev/loop4      218M  218M     0 100% /snap/gnome-3-34-1804/60
        /dev/loop5       63M   63M     0 100% /snap/gtk-common-themes/1506
        /dev/loop6       69M   69M     0 100% /snap/lxd/17629
        /dev/loop0       98M   98M     0 100% /snap/core/9993
        /dev/loop7       56M   56M     0 100% /snap/core18/1885
        /dev/loop8       97M   97M     0 100% /snap/core/9804
        /dev/loop9      261M  261M     0 100% /snap/kde-frameworks-5-core18/32
        /dev/loop10      50M   50M     0 100% /snap/snap-store/467
        /dev/loop11      55M   55M     0 100% /snap/core18/1880
        /dev/loop12      44M   44M     0 100% /snap/snap-store/415
        /dev/loop13      31M   31M     0 100% /snap/snapd/9279
        /dev/loop14      30M   30M     0 100% /snap/snapd/8790
        /dev/sda1       511M  7.8M  504M   2% /boot/efi
        tmpfs           1.0M     0  1.0M   0% /var/snap/lxd/common/ns
        tmpfs           1.6G   28K  1.6G   1% /run/user/1000

So I removed the whole lxd using snap remove lxd

After this, I rebooted my system and although lxd was gone, the disk space is still present somewhere.

/dev/sda2 234G 212G 9.8G 96% /

I re-installed lxd using snap again and ran lxd init, I was not able to find the previous storage pool costorage1, so I created a new one with the default 30G.

 $ lxc storage info storage1
      description: ""
      driver: zfs
      name: storage1
      space used: 620.54kB
      total space: 28.61GB
    used by:
      - default

How can I safely remove that other 150G from the old Btrfs pool from my Linux system?

Thanks for any suggestions.


After careful investigation with @stgraber it resulted that the space was not used by the previous storage pool configured using btrfs. It was actually used by libvirt and KVM images, as I am also running KVM in the same box.

This can be resolved.

Thank you and apologies for the inconvenience.