Enhancing active link utilization in serial attached SCSI topologies

Abstract

Methods and systems are provided for enhanced link utilization in attached SCSI (SAS) topologies. A SAS expander may be configured to monitor link utilization within a SAS topology, and may manage connection requests received thereby based on the monitoring of link utilization. The monitoring may comprise determining availability of links for at least one node within the SAS topology with respect to other nodes in the SAS topology. This may be done based on pending connection requests, and/or responses thereto received by the SAS expander. It may also be done based on shared link utilization data. The managing may comprise determining for each received connection request when link unavailability in other nodes within the SAS topology prevents connectivity to a destination node corresponding to the connection request. When this situation occurs, the SAS expander may handle the connection request directly.

What is claimed is: 
     
       1. A method, comprising:
 in a network device that is configured to provide an expander function within a serial attached SCSI (SAS) topology:
 monitoring link utilization within the SAS topology, wherein the monitoring comprises determining availability of links for at least one node within the SAS topology with respect to other nodes in the SAS topology; and 
 managing connection requests received by the expander function based on the monitoring of link utilization, wherein the managing comprises determining for each received connection request when link unavailability in the other nodes within the SAS topology prevents connectivity to a destination node corresponding to the connection request. 
 
 
     
     
       2. The method of  claim 1 , comprising handling the connection request directly by the expander function in the network device based on the determining that the connectivity to the particular destination node is prevented. 
     
     
       3. The method of  claim 2 , comprising issuing by the expander function messages indicating that the connectivity to the particular destination node is prevented. 
     
     
       4. The method of  claim 1 , comprising determining availability of links within the SAS topology based on messages received from the other nodes in the SAS topology. 
     
     
       5. The method of  claim 4 , wherein the messages received from the other nodes in the SAS topology are responsive to connections requests. 
     
     
       6. The method of  claim 5 , wherein the messages comprise arbitration-in-progress (AIP) responses. 
     
     
       7. The method of  claim 1 , comprising generating and/or maintaining a link availability database by the expander function in the network device, for use in tracking link availability within the SAS topology. 
     
     
       8. The method of  claim 7 , comprising updating the link availability database based on data received from the other nodes in the SAS topology. 
     
     
       9. The method of  claim 1 , comprising communicating link availability related updates to the other nodes in the SAS topology. 
     
     
       10. The method of  claim 9 , comprising communicating the link availability related updates to the other nodes in the SAS topology based on reception, by the expander function, of messages or information that are indicative of link availability or changes thereto. 
     
     
       11. A system, comprising:
 one or more circuits for use in a network device that is configured to provide an expander function within a serial attached SCSI (SAS) topology, the one or more circuits being operable to:
 monitor link utilization within the SAS topology, wherein the monitoring comprises determining availability of links for at least one node within the SAS topology with respect to other nodes in the SAS topology; and 
 manage connection requests received by the expander function based on the monitoring of link utilization, wherein the managing comprises determining for each received connection request when link unavailability in the other nodes within the SAS topology prevents connectivity to a destination node corresponding to the connection request. 
 
 
     
     
       12. The system of  claim 11 , wherein the one or more circuits are operable to handle the connection request directly by the expander function in the network device based on the determining that the connectivity to the particular destination node is prevented. 
     
     
       13. The system of  claim 12 , wherein the one or more circuits are operable to issue by the expander function messages indicating that the connectivity to the particular destination node is prevented. 
     
     
       14. The system of  claim 11 , wherein the one or more circuits are operable to determine availability of links within the SAS topology based on messages received from the other nodes in the SAS topology. 
     
     
       15. The system of  claim 14 , wherein the messages received from the other nodes in the SAS topology are responsive to connections requests. 
     
     
       16. The system of  claim 15 , wherein the messages comprise arbitration-in-progress (AIP) responses. 
     
     
       17. The system of  claim 11 , wherein the one or more circuits are operable to generate and/or maintain a link availability database by the expander function in the network device, for use in tracking link availability within the SAS topology. 
     
     
       18. The system of  claim 17 , wherein the one or more circuits are operable to update the link availability database based on data received from the other nodes in the SAS topology. 
     
     
       19. The system of  claim 11 , wherein the one or more circuits are operable to communicate link availability related updates to the other nodes in the SAS topology. 
     
     
       20. The system of  claim 19 , wherein the one or more circuits are operable to communicate the link availability related updates to the other nodes in the SAS topology based on reception, by the expander function, of messages or information that are indicative of link availability or changes thereto.