How does "btrfs fi show" show full?

[Marc MERLIN <marc@merlins.org>]

More slides, more questions, sorry :)
(thanks for the other answers, I'm still going through them)

If I have:
gandalfthegreat:~# btrfs fi show
Label: 'btrfs_pool1'  uuid: 873d526c-e911-4234-af1b-239889cd143d
	Total devices 1 FS bytes used 214.44GB
	devid    1 size 231.02GB used 231.02GB path /dev/dm-0

I'm a bit confused.

It tells me
1) FS uses 214GB out of 231GB
2) Device uses 231GB out of 231GB

I understand how the device can use less than the FS if you have
multiple devices that share a filesystem.
But I'm not sure how a filesystem can use less than what's being used on
a single device.

Similarly, my current laptop shows:
legolas:~# btrfs fi show
Label: btrfs_pool1  uuid: 4850ee22-bf32-4131-a841-02abdb4a5ba6
	Total devices 1 FS bytes used 442.17GiB
	devid    1 size 865.01GiB used 751.04GiB path /dev/mapper/cryptroot

So, am I 100GB from being full, or am I really only using 442GB out of 865GB?

If so, what does the device used value really mean if it can be that
much higher than the filesystem used value?

Thanks,
Marc
-- 
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Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901