Inside Storage Networking

I recently worked with a customer who had their SAN implemented as depicted in the diagram for a Hyperswap V7000 cluster.   An SVC or FlashSystem cluster that is configured for Hyperswap has half of the nodes at one site, and half of the nodes at the other site.  The I/O groups are configured so that nodes at each site are in the same I/O group.  In the example from the diagram, the nodes at Site 1 were in one I/O group, the nodes at the other were in another I/O group.  A stretched cluster also has the nodes in a cluster at two sites, however each I/O group is made up of nodes from each site.  So for our diagram below,  in a Stretched configuration, a node from Site 1 and a node from Site 2 would be in an I/O Group.   From the diagram we see that each site had two V7000 nodes.  Each node had connections to two switches at each site.  The switches were connected as pictured in the diagram to create two redundant fabrics that spanned the sites.   The customer had hosts and third-p