Inefficient data relocation when removing multiple devices

[frukto]

I have a btrfs consisting of six devices. I am attempting to remove three devices at once using the following command:

btrfs device remove /dev/sda /dev/sdb /dev/sdc /some/mountpoint

There is enough free space available to complete the operation. From what I observe, btrfs removes the devices one at a time. However, while waiting for sda to be removed, I notice that the usage on sdb and sdc actually increases.

I would expect the command to be smarter and preferentially move data to devices that are not scheduled for removal.

[Forza-tng]

There is the metadata/allocator hints patches can do what you want. They are maintained for the LTS kernels (6.12) by kakra

Look at the option 5. Prevent allocating new chunks to this device.

• [6.12] Track btrfs patches kakra/linux#36
• https://wiki.tnonline.net/w/Btrfs/Allocator_Hints