$ sudo su -
$ mkfs.btrfs -f /dev/sdb
$ mkfs.btrfs -f /dev/sdc
$ btrfs fi show
Should give you output something like this:
Cannot analyze code. No Pygments lexer found for “txt”.
.. code-block:: txt Label: none uuid: bfee4bb4-3886-406f-94df-cb2dcf42f044 Total devices 1 FS bytes used 112.00KiB devid 1 size 5.00GiB used 548.00MiB path /dev/sdc Label: none uuid: a0192bd3-a8f7-477b-9bae-fea9a48aa1ab Total devices 1 FS bytes used 2.24GiB devid 1 size 5.00GiB used 3.04GiB path /dev/sdb Btrfs v3.12
$ mkdir /mnt/butter
$ mount /dev/sdb /mnt/butter $ btrfs device add -f /dev/sdc /mnt/butter
$ btrfs fi show
Label: none uuid: a0192bd3-a8f7-477b-9bae-fea9a48aa1ab
Total devices 2 FS bytes used 2.24GiB
devid 1 size 5.00GiB used 3.04GiB path /dev/sdb
devid 2 size 5.00GiB used 0.00 path /dev/sdc
Btrfs v3.12
$ btrfs fi df /mnt/butter
Data, single: total=2.51GiB, used=2.23GiB
System, DUP: total=8.00MiB, used=16.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, DUP: total=256.00MiB, used=2.94MiB
Metadata, single: total=8.00MiB, used=0.00
$ btrfs balance start -v -dconvert=raid1 -mconvert=raid1 /mnt/butter
$ btrfs fi df /mnt/butter
Data, RAID1: total=3.96GiB, used=2.23GiB
System, RAID1: total=32.00MiB, used=16.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, RAID1: total=256.00MiB, used=2.55MiB
$ btrfs fi show
Label: none uuid: a0192bd3-a8f7-477b-9bae-fea9a48aa1ab
Total devices 2 FS bytes used 2.24GiB
devid 1 size 5.00GiB used 4.25GiB path /dev/sdb
devid 2 size 5.00GiB used 4.25GiB path /dev/sdc
$ btrfs balance start -v -dconvert=raid1 -mconvert=raid1 /mnt/btrfs/
Dumping filters: flags 0x7, state 0x0, force is off
DATA (flags 0x100): converting, target=16, soft is off
METADATA (flags 0x100): converting, target=16, soft is off
SYSTEM (flags 0x100): converting, target=16, soft is off
... 10 hours later ...
Done, had to relocate 1269 out of 1269 chunks
$ btrfs fi show
Label: home1 uuid: 43f4a92c-9475-400b-a6e4-88639f55dd71
Total devices 2 FS bytes used 1.23TiB
devid 1 size 1.82TiB used 1.24TiB path /dev/sdb1
devid 2 size 1.82TiB used 1.24TiB path /dev/sdc1
$ btrfs fi df /mnt/btrfs/
Data, RAID1: total=1.23TiB, used=1.23TiB
System, RAID1: total=32.00MiB, used=184.00KiB
Metadata, RAID1: total=6.00GiB, used=2.71GiB
watch -cn 300 btrfs balance status /mnt/btrfs/