SUSE extend system disk

https://www.suse.com/support/kb/doc/?id=000018798

Expanding the file system by adding a new disk

A convenient and quick solution to add disk space to an existing btrfs file system is by adding a new disk. 
The procedure consists of four steps and the system does not need to be rebooted:

1. add a new disk
2. rescan the SCSI bus using 
   
   rescan-scsi-bus.sh -a
   
3. Add the newly added device to the root btrfs filesystem 
   
   btrfs device add /dev/sdX /
   
   
4. At this point the metadata is only stored on the first disk, to distribute (balance) it across the devices run:
   
   btrfs filesystem balance /