Linking two EX4 units as one?

Can i have 2x EX4 units linked together? i am currently looking at getting 1 ex4 in the comming week installed with 4x 6TB drives. can i get a second unit in 3 months and link that to the same unit then having 1 ex4 sharing 8x 6TB drives or will they both be standalone units. 

I think it’s impossible because I can’t imagine how you will connect two EX 4 with Ethernet cables.