---- From: Leszek Dubiel [off-list ref] -- Sent: 2021-05-21 - 18:34 ----

Hello!

Why Btrfs is not using /dev/sdc2?
There is no line "Data,RAID1" for this disk.
Isn't it supposed to use disk that has most of free space?

Thanks for help :) :)
Using Btrfs in production.


Here are some command outputs:



### btrfs fi show /

Label: none  uuid: ea6ae51d-d9b0-4628-a8f3-3406e1dc59c6
     Total devices 4 FS bytes used 2.96TiB
     devid    1 size 7.25TiB used 3.20TiB path /dev/sda2
     devid    2 size 7.25TiB used 3.20TiB path /dev/sdb2
     devid    3 size 7.25TiB used 3.21TiB path /dev/sdd2
     devid    4 size 7.25TiB used 32.00MiB path /dev/sdc2



### btrfs fi df /

Data, RAID1: total=4.49TiB, used=2.90TiB
System, RAID1: total=64.00MiB, used=784.00KiB
Metadata, RAID1: total=321.00GiB, used=56.08GiB
GlobalReserve, single: total=512.00MiB, used=0.00B



### btrfs dev usa /

/dev/sda2, ID: 1
    Device size:             7.25TiB
    Device slack:              0.00B
    Data,RAID1:              2.99TiB
    Metadata,RAID1:        210.00GiB
    System,RAID1:           64.00MiB
    Unallocated:             4.05TiB

/dev/sdb2, ID: 2
    Device size:             7.25TiB
    Device slack:              0.00B
    Data,RAID1:              3.00TiB
    Metadata,RAID1:        210.00GiB
    Unallocated:             4.04TiB

/dev/sdc2, ID: 4
    Device size:             7.25TiB
    Device slack:              0.00B   ... no Data/RAID1
    System,RAID1:           32.00MiB
    Unallocated:             7.25TiB

/dev/sdd2, ID: 3
    Device size:             7.25TiB
    Device slack:              0.00B
    Data,RAID1:              2.99TiB
    Metadata,RAID1:        222.00GiB
    System,RAID1:           32.00MiB
    Unallocated:             4.04TiB



### time btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft /

Done, had to relocate 0 out of 4922 chunks

real    0m0,522s
user    0m0,000s
sys    0m0,033s

Raid1 means two copies on different devices. This is fulfilled with the previous 3 drives so the  'soft' keyword is not going to help here. 

You can do a full data balance (-dusage=100) to move some data across to the new disk. There is no need to do a metadata balance in this case, unless you want to convert to raid1c3 to have three copies of metadata. 

If you do nothing, the filesystem will eventually balance itself as you add abs delete data. 

https://btrfs.wiki.kernel.org/index.php/Balance_Filters