DATE CHECKED THIS PAGE WAS VALID: 14/09/2023 

If you created your BTRFS filesystem a little while ago you might not have no_holes support which is simply an improvement that can be added and reduces the size metadata consumes on the disk. You can check if your filesystem has it in 2 ways:

1)
<code>
sudo btrfs inspect-internal dump-super /dev/nvme0n1p2
</code>

where /dev/<disk> is what you want to check.

Output is as follows:
{{:images:noholesbtrfs.png|}}
 
As you can note, NO_HOLES is listed under incompat_flags.

Another method is to check via the UUID in this way:
<code>
ls /sys/fs/btrfs/383732b1-5e87-4b68-a15a-f044bc559877/features/
</code>
{{:images:noholesbtrfs2.png|}}

As we can see no_holes is also listed here.

To add no_holes support the disk must be UNMOUNTED. This might mean you have to boot off a live CD like an ubuntu live ISO from a USB stick. 

Once you have unmounted the filesystem you can easily add no_holes support with the -n flag as such:
<code>
sudo btrfstune -n /dev/nvme0n1p2
</code>

Note, as that disk housed my root partition I had to use a live CD in order to run the command successfully then reboot back into my system afterwards.

This completes how to add the no_hole improvement to a filesystem made prior to v5.15 when it became the default.