Able to link two EX2100's?

I currently use two EX2100’s. One for my file storage/media server and the other for a backup.

I plan to upgrade my primary nas to a 4 bay model soon. Is there a way to link my two existing EX2100’s together so when I do a backup of my new nas it will look at them as one large device? Or will I have to choose to backup half of my 4 bay nas to one ex2100 and the other half to the second ex2100? Thank you

Thank you for the information, will help me plan out my upgrade path going forward. Appreciate you taking the time to reply. Cheers!