1. Rack mount the New disk shelf (xx TB)
Whenever i have added a disk shelf i have taken the whole system down first as we are plugging in SAS cables here - so i like to work on the safe side and this also ensure the bus is fully scanned too.
2. Connect the SAS cables from new Disk shelf (2*SAS IN) to the existing Appliance disk shelf (2* SAS out ports)
3. Power ON New disk shelf and wait for 10-20 mins to let initialize the disk shelf completely.
Depending on your configuration (Master/Media) (Advanced Disk Pool / Dedupe Pool) you'll have the following partitions (volumes) available.
Once you add the new tray you'll get an extra disk (highlighted below)
Usually I prefer doing it from Web GUI
Ex:- manage > storage > add unit_3 to grow your respective pool