Chapter 13. RAS, monitoring, and troubleshooting 679
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. 
Figure 13-4   Concept of SAS chaining