expansion and failover

[jchen522]

Connect and Activate the Expansion Shelf

https://support.hpe.com/hpesc/public/docDisplay?docId=sd00006088en_us&page=GUID-C001824F-524C-4903-AB06-42EBA0BF68B0.html

Please see diagram. 
We currently have A, B, C in production and want to connect and add D into the expansion.

I was wondering if someone can explain how does expansion and failover work in this scenario. 

What is the procedure for adding D into production?
How many units/controllers/path can fail and still stays up?
What happens if unit B totally dies?  There doesn't seem to be a connection for SAS D going back to A in a loop.  Or it doesn't work that way?

Thank you.