Each engine has two director board installed.  Each engine has 8 backend loops for drive connections that can go up to 5 drive bays deep in some configurations.   If you add more than 2 drive bays to the first four engines, you cannot add more than 4 engines to the configuration (it is then a deep daisy chained config).  The normal performance configurations allow two drive bays on the 1st four engines, and three drive bays on the 2nd four engines.  Each director board has two IO modules that can be selected by the customer.  For example you could install all fiber channel IO modules and get 16 FA ports per engine.  
VMAX-1/ 5874.207.166  In SYM we can figure out how many drives(Drive Bays) or host connections  will be supported looking at the number of Directors availble. With VMAX the Enigines(Single , Dual) concept came.  How can i determin how many engines my VMAX currently have? How many more it can support if needed? Is there a relation between the number of engnies &  directors in VMAX?
How to determine number of engines in vmax