Balancing the btrfs filesystem
If the need to add the additional disk to the volume was due to it running out of disk space, then we may choose to help performance by spreading the data across both devices. This is achieved using the balance subcommand:
# btrfs filesystem balance start -d -m /data/simple
The -m argument represents metadata and -d represents data. In this way, the disks are used at an equal ratio.
The output from the demonstration system is shown in the following command; note that you can omit filesystem from the balance subcommand because it's optional in this case:
