text: A strand starts with an SAS initiator chip inside an IBM Storwize V7000 node canister and 
  progresses through SAS expanders, which connect disk drives. Each canister contains an 
  expander. Each drive has two ports, each connected to a different expander and strand. This 
  configuration ensures that both nodes in the input/output (I/O) group have direct access to 
  each drive, and that is no single point of failure exists. 
  
  Figure 13-4 shows how the SAS connectivity works inside the node and expansion canisters. 