Simple commands to setup a BTRFS filesystem across multiple disks as a JBOD implementation.

# Create a filesystem across the drives (metadata mirrored, linear data allocation)
sudo mkfs.btrfs -f -L MEDIA -d single -m raid1 /dev/mapper/data-*

To show all the filesystems

sudo btrfs filesystem show

To check filesystem usage

sudo btrfs filesystem df /mnt/media

In order to then add a disk to this filesystem later

sudo btrfs device add /dev/sdb /mnt/media
btrfs filesystem balance /mnt/media

We can also convert another btrfs filesystem data allocation (e.g. RAID1) to single as part of the balance process.

sudo btrfs balance start -dconvert=single,soft /mnt/media