Translations:Btrfs/59/en
From Manjaro
Balance ⇒
When adding devices or changing the RAID-level of your volume, it may be necessary to balance your volume. While balancing, btrfs will read ALL (or a subset of all) chunks in, and write them out again using the actual RAID-level. It will stripe these files over all available devices equally. While this happens, the volume will keep being usable, but you may see some heavy load on it. Also this may take a very long time because ALL data must be read AND written again. Don´t worry about shutdown. When you shutdown your computer while the balance is running, the balance will pause. After you restart the computer the balance will restart and continue until it is finished.