Re: support request: btrfs df reports drive is out of space, cannot find what occupies it

[Skirnir Torvaldsson <skirnir.torvaldsson@gmail.com>]

With all due respect, 38G is a grand total, so it is 38G out of 78G 
reported data.
There is one thing I've noticed that troubles me:

root@next:/home/support/btrfs-list-2.3# ./btrfs-list
NAME                      TYPE    REFER     EXCL  MOUNTPOINT
NEXT_ROOTFS                 fs       -    78.37G (single/dup, 
15.03G/95.46G free, 15.74%)
    [main]              mainvol   16.00k   16.00k /
    @System              subvol   16.00k   16.00k /.snapshots
    @Logs                subvol   16.00k   16.00k /next/logs/.snapshots
    @Logs/current        subvol    4.70G    4.70G /next/logs
    @AppData             subvol   16.00k   16.00k /next/appdata/.snapshots
    @AppData/current     subvol  370.14M  370.14M /next/appdata
    @AppData/var         subvol   16.00k   16.00k
    @Databases           subvol   16.00k   16.00k /next/databases/.snapshots
    @Databases/current   subvol  754.95M  754.95M /next/databases
    @MessageBus          subvol   16.00k   16.00k /next/mbus/.snapshots
    @MessageBus/current  subvol   67.70G   67.70G /next/mbus
    @Updates             subvol   16.00k   16.00k /next/updates/.snapshots
    @Updates/current     subvol    1.81G    1.81G /next/updates
    @SystemData          subvol   16.00k   16.00k 
/next/systemdata/.snapshots
    @SystemData/current  subvol    1.21G    1.21G /next/systemdata
    @System/prev         subvol    1.48G    1.48G
    @System/current      subvol  443.27M  443.27M /
root@next:/home/support/btrfs-list-2.3# du -hd1 /next/mbus
0       /next/mbus/.snapshots
1.4G    /next/mbus/redpanda
1.4G    /next/mbus

So, the MessageBus subvolume is occupying 67Gb (?), however I fail to 
understand how come this space is not accounted for by du and how I can 
clean it and limit it in future.

> On Fri, Apr 19, 2024 at 11:40 AM Skirnir Torvaldsson
> <skirnir.torvaldsson@gmail.com> wrote:
>> Dear btrfs experts,
>>
>> Could you please help me sort out the following situation:
>>
>> btrfs df reports my 100Gb device is almost out of space (which agrees with the results produced by the standard "df"):
>>
>> root@next:/home/support# btrfs fi df /
>> Data, single: total=82.00GiB, used=78.23GiB
>> System, DUP: total=32.00MiB, used=16.00KiB
>> Metadata, DUP: total=1.00GiB, used=153.70MiB
>> GlobalReserve, single: total=68.45MiB, used=0.00B
>> root@next:/home/support# df -h /
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/sda3        96G   79G   16G  84% /
>>
>> However  when I try to locate files to delete with du that's what I get:
>>
>> root@next:/home/support# du -hd1 /
>> 70M     /boot
>> 0       /dev
>> 2.2G    /.snapshots
>> 14M     /bin
>> 4.5M    /etc
>> 2.5M    /home
>> 348M    /lib
>> 4.0K    /lib64
>> 0       /media
>> 0       /mnt
>> 0       /opt
>> 0       /proc
>> 40K     /root
>> 2.7M    /run
>> 12M     /sbin
>> 0       /srv
>> 0       /sys
>> 0       /tmp
>> 566M    /usr
>> 5.0G    /var
>> 29G     /next
>> 38G     /
>>
>> I.e. almost 40Gb just gone somewhere.
> Huh?
>
> 2.2G + 5.0G + 29G + 38G == 75.2G out of 78G reported for DATA. What
> 40G are you talking about?
>
> If you have some other mount points, you could start with explaining
> your storage layout first.
>
>> Am I doing something wrong? Is there a problem or a piece of theory I'm missing? Kindly advice.
>>
>> +++++++++++++++++++++++++++++++++++++
>> root@next:~#  uname -a
>> Linux next 5.10.0-28-amd64 #1 SMP Debian 5.10.209-2 (2024-01-31) x86_64 GNU/Linux
>> root@next:~#  btrfs --version
>> btrfs-progs v5.10.1
>> root@next:~#  btrfs fi show
>> Label: 'NEXT_ROOTFS'  uuid: abc71bdb-c570-461d-a28a-54294a646089
>>          Total devices 1 FS bytes used 78.37GiB
>>          devid    1 size 95.46GiB used 84.06GiB path /dev/sda3
>>
>> root@next:~#  btrfs fi df /
>> Data, single: total=82.00GiB, used=78.22GiB
>> System, DUP: total=32.00MiB, used=16.00KiB
>> Metadata, DUP: total=1.00GiB, used=153.64MiB
>> GlobalReserve, single: total=68.45MiB, used=0.00B
>>