SAS expander based persistent connections

A network device comprising:

• a first attach point circuit for connecting the network device to a first physical link, the first attach point circuit comprising a first cache memory;
• a second attach point circuit for connecting the network device to a second physical link, the second attach point circuit comprising a second cache memory;
• a physical switch for connecting the first attach point circuit and the second attach point circuit to each other;
• and
• persistent connection logic configured to create a persistent connection between a first network element and a second network element, the persistent connection comprising the network device, the first physical link, and the second physical link, the persistent connection enabling cache coherency between the first cache memory and the second cache memory,
• wherein the network device is operable to implement a non-persistent connection between two network elements, the non-persistent connection comprising at least the network device, the non-persistent connection being removable according to a CLOSE message or a BREAK message, and the persistent connection being removable according to a link reset message, wherein the link reset message is different than the CLOSE message or the BREAK message.

An apparatus comprising:

• a controller for sending commands to one or more network devices for setting up a persistent connection between a first network element and a second network element,
• wherein the one or more network devices comprises:
• a first attach point circuit for connecting to a first physical link, the first attach point circuit comprising a first cache memory;
• and
• a second attach point circuit for connecting to a second physical link, the second attach point circuit comprising a second cache memory,
• wherein the persistent connection comprises the one or more network devices and the first physical link and the second physical link, the persistent connection being removable according to a link reset message, the persistent connection enabling cache coherency between the first cache memory and the second cache memory,
• wherein at least one of the one or more network devices is operable to implement a non-persistent connection between two network elements, the non-persistent connection comprising said at least one network device, the non-persistent connection being removable according to a CLOSE message or a BREAK message, wherein the link reset message is different than the CLOSE message or the BREAK message.

A network comprising:

• a first cascade of one or more expander circuits comprising a first root switch expander circuit for connecting to a first initiator, an expander circuit of the first cascade operable to connect to a target, the first cascade of one or more expander circuits comprising a first cache memory;
• a second cascade of one or more expander circuits including a second root switch expander circuit for connecting to a second initiator, the second cascade of one or more expander circuits comprising a second cache memory,
• wherein the first root switch expander circuit and the second root switch expander circuit are configured to create a persistent connection between the second initiator and the target through the first root switch expander circuit and the second root switch expander circuit, the persistent connection being removable according to a link reset message, the persistent connection enabling cache coherency between the first cache memory and the second cache memory,
• wherein the first root switch expander circuit and the second root switch expanders are operable to implement a non-persistent connection between the second initiator and the target through the first root switch expander circuit and the second root switch expanders, the non-persistent connection being removable according to a CLOSE message or a BREAK message, wherein the link reset message is different than the CLOSE message or the BREAK message.