I have had problems with my 40GB root partition and want to transfer space from a second 400GB partition. I have BTRFS installed on top of LVM. For some reason, OpenSUSE decided this for me an installation time and I considered it made sense:# lsblkNAME            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTsda               8:0    0 464.5G  0 disk `-sda1            8:1    0 464.5G  0 part   |-system-swap 254:0    0     2G  0 lvm  [SWAP]  |-system-root 254:1    0    40G  0 lvm  /  `-system-opt  254:2    0 422.5G  0 lvm  /optLVMsr0              11:0    1  1024M  0 rom  # btrfs filesystem showLabel: none  uuid: 681e689d-1ac2-48ac-9fba-f6a6e234e9f5    Total devices 1 FS bytes used 28.40GiB    devid    1 size 40.00GiB used 35.53GiB path /dev/mapper/system-rootLabel: none  uuid: 90b22bed-5924-425d-ac30-03279f970fa0    Total devices 1 FS bytes used 159.43GiB    devid    1 size 300.00GiB used 299.04GiB path /dev/mapper/system-optAs you see, /dev/mapper/system-opt only has 300GB, so I have 100 GB free there as I did a btrfs resize to free 100 GB.My problem is that I don't know how to add those 100GB into / directory (/dev/mapper/system-root). I have tried:# btrfs device add /dev/mapper/system-opt //dev/mapper/system-opt appears to contain an existing filesystem (btrfs).Use the -f option to force overwrite.It seems OpenSUSE formats btrfs on top of dm-1 and dm-2 which probably map to LVM volumes.# btrfs device usage //dev/dm-1, ID: 1   Device size:            40.00GiB   Data,single:            33.00GiB   Metadata,single:         2.50GiB   System,single:          32.00MiB   Unallocated:             4.47GiB# btrfs device usage /optLVM/dev/dm-2, ID: 1   Device size:           422.50GiB   Data,single:           297.01GiB   Metadata,single:         8.00MiB   Metadata,DUP:            2.00GiB   System,single:           4.00MiB   System,DUP:             16.00MiB   Unallocated:           988.00MiBCan I do? btrfs device add /dev/dm-2 /To make / (root btrfs partition) get the Unallocated 100GB in the dm-2 partition?
Advice on how to transfer space in a BTRFS setup
opensuse;lvm;btrfs