2.2.2 Basic core-edge topology The core-edge topology (as shown in Figure 2-3) is easily recognized by most SAN  architects. This topology consists of a switch in the center (usually, a director-class switch),  which is surrounded by other switches. The  core switch  contains all FlashSystem and  high-bandwidth hosts. It is connected by using ISLs to the edge switches. The edge switches  can be of any size from 24 port switches up to multi-slot directors.  When the FlashSystem and servers are connected to different switches, the hop count for this  topology is one. Figure 2-3 Core-edge topology 16  IBM FlashSystem 9200 and 9100 Best Practices and Performance Guidelines