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I cannot shrink btrfs filesystem although there is still data and metadata space left :

$ sudo btrfs filesystem resize -11G /home;echo $?

Resize '/home' of '-11G'

ERROR: unable to resize '/home': No space left on device

1

Here are some btrfs filesystem info about /home :

$ sudo btrfs filesystem df /home | column -t

Data,           single:  total=92.01GiB,   used=80.68GiB

System,         DUP:     total=8.00MiB,    used=16.00KiB

System,         single:  total=4.00MiB,    used=0.00B

Metadata,       DUP:     total=1.00GiB,    used=631.41MiB

Metadata,       single:  total=8.00MiB,    used=0.00B

GlobalReserve,  single:  total=224.00MiB,  used=0.00B

$ sudo btrfs filesystem show /home

Label: none  uuid: c7ee56a8-ef45-46c8-86d1-13879201a1e7

    Total devices 1 FS bytes used 81.30GiB

    devid    1 size 100.00GiB used 94.04GiB path /dev/mapper/home_VG-home



$ sudo btrfs filesystem usage -T /home

Overall:

    Device size:         100.00GiB

    Device allocated:         94.04GiB

    Device unallocated:        5.96GiB

    Device missing:          0.00B

    Used:             81.91GiB

    Free (estimated):         17.29GiB  (min: 14.31GiB)

    Data ratio:               1.00

    Metadata ratio:           1.99

    Global reserve:      224.00MiB  (used: 0.00B)



             Data     Metadata Metadata  System  System              

Id Path      single   single   DUP       single  DUP      Unallocated

-- --------- -------- -------- --------- ------- -------- -----------

 1 /dev/dm-0 92.01GiB  8.00MiB   2.00GiB 4.00MiB 16.00MiB     5.96GiB

-- --------- -------- -------- --------- ------- -------- -----------

   Total     92.01GiB  8.00MiB   1.00GiB 4.00MiB  8.00MiB     5.96GiB

   Used      80.68GiB    0.00B 631.41MiB   0.00B 16.00KiB            

and here the output of dmesg :

$ dmesg | tail -11

[44202.411949] BTRFS info (device dm-0): new size for /dev/dm-0 is 97706311680

[44202.412156] BTRFS info (device dm-0): relocating block group 120288444416 flags 1

[44208.119721] BTRFS info (device dm-0): relocating block group 119214702592 flags 1

[44211.611669] BTRFS info (device dm-0): relocating block group 118140960768 flags 1

[44212.495603] BTRFS info (device dm-0): relocating block group 117067218944 flags 1

[44213.006830] BTRFS info (device dm-0): relocating block group 95592382464 flags 1

[44216.613870] BTRFS info (device dm-0): relocating block group 120288444416 flags 1

[44222.780073] BTRFS info (device dm-0): relocating block group 119214702592 flags 1

[44225.843279] BTRFS info (device dm-0): relocating block group 118140960768 flags 1

[44226.575236] BTRFS info (device dm-0): relocating block group 117067218944 flags 1

[44226.930918] BTRFS info (device dm-0): relocating block group 95592382464 flags 1

Can you help me ?

You're requesting the volume to shrink by 11GB, yet you only have about 6GB unallocated.

You can more efficiently use allocated extents by rebalancing the volume. Executing a command similar to btrfs balance start /home will start that process, and it may take some time to complete.

But I don't know if that will free up enough for a large amount of shrinkage.