Sas expander based persistent connections

Abstract

Embodiments of the present invention provide for creating and using persistent connections in SAS networks. A persistent connection may be a connection that persists for longer than the usual SAS connection. More specifically, it is a connection that is not subject to periodic tear downs by SAS devices according to existing SAS protocols (such as, by using CLOSE or BREAK primitives). Instead, persistent connections may be removable bra link reset Persistent connections may be used in situations in which the overhead associated with the usual tear down and re-establishment of connections in a SAS network may be considered too high in comparison with its intended benefits. Persistent connections way also be used to provide virtual direct attachment between two different SAS connected devices or between a SAS connected device and an expander.

1 - 22 . (canceled) 
     
     
         23 . A network device, comprising:
 a first memory;   a second memory; and   a first switch circuit operably coupled to the first cache memory; and   a second switch circuit operably coupled to the first switch circuit and operably coupled to the second memory, the first switch circuit and second switch circuit being configured as a persistent connection between the first memory and the second memory, the persistent connection enabling cache coherency between the first memory and the second memory.   
     
     
         24 - 27 . (canceled) 
     
     
         28 . The network device of  claim 23 , wherein the persistent connection enables virtual access to a storage device. 
     
     
         29 . The network device of  claim 23 , wherein the persistent connection simulates a direct connection between a target device and an initiating device. 
     
     
         30 . The network device of  claim 23 , wherein the persistent connection is a non-interruptible link between the first memory and the second memory. 
     
     
         31 . The network device of  claim 23 , wherein the persistent connection is a virtual link between the first memory and the second memory. 
     
     
         32 . The network device of  claim 23 , wherein the first switch circuit is a first expander and the second switch circuit is a second expander. 
     
     
         33 . A network device, comprising:
 a first interface to an initiating device;   a second interface to a target device;   a first switch circuit operably coupled to the first interface; and   a second switch circuit operably coupled to the first switch circuit and operably coupled to the second interface, the first switch circuit and second switch circuit being configured as a persistent connection between the initiating device and the target device, the persistent connection enabling cache coherency between the initiating device and the target device.   
     
     
         34 . The network device of  claim 33 , wherein the persistent connection enables virtual access to a storage device. 
     
     
         35 . The network device of  claim 33 , wherein the persistent connection simulates a direct connection between the target device and the initiating device. 
     
     
         36 . The network device of  claim 33 , wherein the persistent connection is a non-interruptible link between a first memory and a second memory. 
     
     
         37 . The network device of  claim 33 , wherein the persistent connection is a virtual link between the target device and the initiating device. 
     
     
         38 . The network device of  claim 33 , wherein the first switch circuit is a first expander and the second switch circuit is a second expander. 
     
     
         39 . A method for network communication, the method comprising:
 connecting a first switch circuit to an initiating device;   connecting a second switch circuit to a target device; and   establishing a persistent connection between the first switch circuit and the second switch circuit, the initiator being operably coupled to the target via the persistent connection.   
     
     
         40 . The method of  claim 39 , wherein the persistent connection simulates a direct connection between the target device and the initiating device. 
     
     
         41 . The method of  claim 39 , wherein the establishing of the persistent connection comprises:
 forwarding an identify message from the initiating device to the target device; and   forwarding an identify message from the target device to the initiating device.   
     
     
         42 . The method of  claim 39 , wherein the method comprises closing the persistent connection by sending a link reset message. 
     
     
         43 . The method of  claim 39 , wherein the initiating device is an input output controller (IOC). 
     
     
         44 . The method of  claim 39 , wherein the target device is a memory device. 
     
     
         45 . The method of  claim 39 , wherein the persistent connection is a non-interruptible link between the initiating device and the target device. 
     
     
         46 . The method of  claim 39 , wherein the persistent connection is a virtual link between the initiating device and the target device.