understanding disk usage on BTRFS

I'm running a small server with BTRFS on a single system SSD and with several additional HDs also with BTRFS but they are not part of my problem. Several months ago I switched from ZFS to BTRFS and with ZFS disk usage always gave plausible values. I have used quite many snapshots and I think I understand how disk usage is affected by snapshots and copy on write.

With BTRFS "df" shows me that the 1 TB SSD is almost full but if I add the used space on all subvolumes I only get about half of that (duplication of data should be deactivated...).

See output of "df -k":

Code:Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda2 971518976 964439664 4599152 100% /If I try to list the sonsumed space on all volumes on this drive with
Code:time find / -maxdepth 4 -type d -inum 256 -print -exec btrfs subvolume show -g '{}' ';'I get the following which does not sum up to what "df -k" reported (result is only about half of that):

Code:rootdir
Name: rootdir
UUID: 61e8dc1c-8ec3-4f4d-bf91-9216e3ce8c88
Parent UUID: -
Received UUID: -
Creation time: 2023-01-30 02:35:13 +0100
Subvolume ID: 265
Generation: 1075247
Gen at creation: 15
Parent ID: 5
Top level ID: 5
Flags: -
Send transid: 0
Send time: 2023-01-30 02:35:13 +0100
Receive transid: 0
Receive time: -
Snapshot(s):
Quota group: 0/265
Limit referenced: -
Limit exclusive: -
Usage referenced: 271.25GiB
Usage exclusive: 271.25GiB
/backup/bbbbbbb
homedir_nobackup/backup_bbbbbbb
Name: backup_bbbbbbb
UUID: fcc88679-0025-ac46-b123-e4a67bf01eea
Parent UUID: -
Received UUID: -
Creation time: 2023-01-30 02:33:53 +0100
Subvolume ID: 260
Generation: 1073469
Gen at creation: 10
Parent ID: 259
Top level ID: 259
Flags: -
Send transid: 0
Send time: 2023-01-30 02:33:53 +0100
Receive transid: 0
Receive time: -
Snapshot(s):
Quota group: 0/260
Limit referenced: -
Limit exclusive: -
Usage referenced: 0.00GiB
Usage exclusive: 0.00GiB
/home
homedir
Name: homedir
UUID: 78ec4fd7-1d93-1e4e-9d15-40a2cc799625
Parent UUID: -
Received UUID: -
Creation time: 2023-01-30 02:32:42 +0100
Subvolume ID: 258
Generation: 1075247
Gen at creation: 8
Parent ID: 5
Top level ID: 5
Flags: -
Send transid: 0
Send time: 2023-01-30 02:32:42 +0100
Receive transid: 0
Receive time: -
Snapshot(s):
Quota group: 0/258
Limit referenced: -
Limit exclusive: -
Usage referenced: 26.67GiB
Usage exclusive: 26.66GiB
/home/ccccccc/dddddd
homedir_nobackup/ccccccc/dddddd
Name: dddddd
UUID: eba49320-154f-b742-90fb-15198e499765
Parent UUID: -
Received UUID: -
Creation time: 2023-01-30 02:34:06 +0100
Subvolume ID: 262
Generation: 1074998
Gen at creation: 12
Parent ID: 261
Top level ID: 261
Flags: -
Send transid: 0
Send time: 2023-01-30 02:34:06 +0100
Receive transid: 0
Receive time: -
Snapshot(s):
Quota group: 0/262
Limit referenced: -
Limit exclusive: -
Usage referenced: 16.46GiB
Usage exclusive: 16.46GiB
/home/eeeeeeeeee/ffffffff
homedir_nobackup/eeeeeeeeee/ffffffff
Name: ffffffff
UUID: b3a70b0c-d227-9a45-9972-8615645b087f
Parent UUID: -
Received UUID: -
Creation time: 2023-01-30 02:34:19 +0100
Subvolume ID: 264
Generation: 1075003
Gen at creation: 14
Parent ID: 263
Top level ID: 263
Flags: -
Send transid: 0
Send time: 2023-01-30 02:34:19 +0100
Receive transid: 0
Receive time: -
Snapshot(s):
Quota group: 0/264
Limit referenced: -
Limit exclusive: -
Usage referenced: 136.78GiB
Usage exclusive: 136.78GiBWhy is my SSD full and what consumes the additional space? And how can I get a better understanding of the consumed space on the disk?