Disk storage not included in the btrfs filesystem du calculations

This document (000021160) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 15

Situation

Based on the output below, the btrfs filesystem df command indicates that the used data usage on the filesystem is approximately 19.65 GB. There is no /.snapshot directory that can be deleted, and none of the other directories are consuming a significant amount of space. Additionally, the output of the btrfs filesystem du --kbytes -s /* command appears to show that the used disk space is actually approximately 6 GB.

# btrfs filesystem df /
Data, single: total=21.00GiB, used=19.65GiB
System, single: total=32.00MiB, used=16.00KiB
Metadata, single: total=768.00MiB, used=482.00MiB
GlobalReserve, single: total=68.08MiB, used=0.00

# /usr/bin/snapper -c root list
 # | Type   | Pre # | Date                     | User | Used Space | Cleanup | Description           | Userdata
---+--------+-------+--------------------------+------+------------+---------+-----------------------+---------
0  | single |       |                          | root |            |         | current               |         
1* | single |       | Wed Mar  3 01:55:46 2021 | root |   2.03 GiB |         | first root filesystem |       

# btrfs filesystem du --kbytes -s /*
Total   Exclusive  Set shared  Filename
1624.00KiB   196.00KiB  1428.00KiB  /bin
118328.00KiB  73056.00KiB  45272.00KiB  /boot
14044.00KiB  7996.00KiB  6048.00KiB  /etc
892324.00KiB  710208.00KiB  182116.00KiB  /lib
11044.00KiB  8008.00KiB  3036.00KiB  /lib64
0.00KiB     0.00KiB     0.00KiB  /media
0.00KiB     0.00KiB     0.00KiB  /mnt
2078008.00KiB  1464520.00KiB  613488.00KiB  /opt
21412.00KiB  20260.00KiB  1152.00KiB  /root
8108.00KiB  2700.00KiB  5408.00KiB  /sbin
0.00KiB     0.00KiB     0.00KiB  /selinux
0.00KiB     0.00KiB     0.00KiB  /srv
34324.00KiB  34324.00KiB     0.00KiB  /tmp
2588100.00KiB  1207620.00KiB  1380480.00KiB  /usr
860472.00KiB  387376.00KiB  473096.00KiB  /var
84088.00KiB     0.00KiB  84088.00KiB  /veeamplugin

Resolution

The btrfs subvolume list command may help provide guidance in situations where users are unable to locate directories or files that are consuming disk space within the btrfs filesystem.

As one example of this, the following output indicates that the missing space is being utilized by the /.veeam_snapshots/ sub-volume snapshots, which are not accounted for in the btrfs filesystem du command calculations. In such cases, we recommend involving the software vendor's support for assistance on how to address and reduce disk space usage.

# btrfs subvolume list /
ID 256 gen 2430144 top level 5 path @
ID 257 gen 2432807 top level 256 path @/var
ID 258 gen 2430772 top level 256 path @/usr/local
ID 259 gen 2432807 top level 256 path @/tmp
ID 260 gen 2430772 top level 256 path @/srv
ID 261 gen 2432805 top level 256 path @/root
ID 262 gen 2432807 top level 256 path @/opt
ID 263 gen 2430772 top level 256 path @/boot/grub2/x86_64-efi
ID 264 gen 2432719 top level 256 path @/boot/grub2/i386-pc
ID 265 gen 2430473 top level 256 path @/.snapshots
ID 266 gen 2432807 top level 265 path @/.snapshots/1/snapshot
ID 11656 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/261_root
ID 11657 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/262_opt
ID 11658 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/259_tmp
ID 11659 gen 2430156 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/265_.snapshots
ID 11660 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/263_x86_64-efi
ID 11661 gen 2430144 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/260_srv
ID 11662 gen 2430144 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/256_@
ID 11663 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/257_var
ID 11664 gen 2430144 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/5_
ID 11665 gen 2430144 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/264_i386-pc
ID 11666 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/266_snapshot
ID 11667 gen 2430454 top level 5 path .veeam_snapshots/{60a425c9-b3c1-4e74-8ced-b910e8c402f3}/258_local
ID 11668 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/261_root
ID 11669 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/262_opt
ID 11670 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/259_tmp
ID 11671 gen 2430144 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/256_@
ID 11672 gen 2430144 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/264_i386-pc
ID 11673 gen 2430144 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/260_srv
ID 11674 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/263_x86_64-efi
ID 11675 gen 2430144 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/265_.snapshots
ID 11676 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/258_local
ID 11677 gen 2430454 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/257_var
ID 11678 gen 2430144 top level 5 path .veeam_snapshots/{515b9e2b-b08c-4e1c-b148-b722d80e1526}/5

Cause

Sometimes there are files underneath mount points which use btrfs disk space, and are also inaccessible from du or btrfs filesystem du command.

Disclaimer

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