Enabling sas expander loops for increased fairness and performance

Abstract

The use of loops in SAS networks is enabled by designating ports connected to loop connections as table loop ports (TLPs). Under normal operating conditions, each TLP is blocked from receiving BCNs, appears to the expander to have nothing connected to it, and is made invisible to initiators. The loop connection and TLPs may be enabled and used to access devices when a problem is detected. In particular, the TLP will now appear in a list of destination ports within the expander to which a BCN should be propagated. In addition, during a subsequent self-configuration, the TLP is allowed to populate its route table with devices accessible through it, and the existence of the TLP is also reported back to initiators. After re-discovery is complete, communications between the initiator and a target can resume, with traffic re-routed through the TLPs as needed, bypassing the failure point.