Had a 3 TB home drive for 2 years, now I needed another one, so I bought a 4TB one to expand my storage and logically I assumed it would just add in to the app and all as a second unit as thats the only reasonable thing to assume.
It seems that I was dead wrong, that WD didnt make their “home” product anything like home friendly and easy to usse, because I had to create a second account to use it!
Seriously, now im sitting here with what is basically an overpriced external harddisk in a fancy box, because that drive does nothing now that an external harddisk wouldnt do, which is being shared across my LAN.
What it should do, is at least show in the WD desktop app and also be shown within the same online account.
Further, it should be possible to enable a overflow mode, so that itll start using the next drive once the first one getss filled up to a certain percentage or maybe do even spanning, like RAID 0.
Its no less than VERY disappointing, that a product intended an affordable home NAS solution, that anyone can implement regardless of geek level, doesnt support something as simple as “more than one unit” as its knmown throughout all computing history, that data accumulates over time for far most users, hence the demand for external USB connected harddrives.
Nowadays we need cloud access and therefore, the Cloud drives should be replacing the common external harddrives, but then WD finds it appropriate to make such a limited design here. 
