System, machine, and method for maintenance of mirrored datasets through surrogate writes during storage-area network transients

A node for connection to a storage area network comprising

• hardware for transmission of frames;
• hardware for reception of frames;
• memory;
• at least one processor for processing frames, the processor coupled to the hardware for transmission of frames, the hardware for reception of frames, and the memory for storage of frames;
• wherein the processor is capable of inspecting frames for encapsulated write requests and, if encapsulated write request frames are found, de-encapsulating the write request and forwarding the write request through the hardware for transmission of frames to a target node of the write request.

A computer network comprising:

• a first node;
• a second node;
• a first target node;
• network interconnect providing communication between the first node and the second node, and providing communication between the second node and the first target node;
• wherein the second node is capable of inspecting incoming frames for encapsulated write requests and, if encapsulated write request frames are found, de-encapsulating a write request from the encapsulated write request frames and forwarding the write request to the first target;
• and
• wherein the second node further is capable of inspecting frames received from the first target node for responses to previously forwarded encapsulated write requests and, when responses to previously forwarded encapsulated write requests are found, forwarding the responses to the first node.

A method of performing writes by a first node of a storage area network to a mirrored dataset, the dataset comprising a first copy on a first storage node of the storage area network and a second copy on a second node of the storage area network, the storage area network having a surrogate-capable node, the method comprising the steps of:

• checking a status of a first path from the node to the first storage node and of a second path from the node to the second storage node;
• the first path has good status and the second path has bad status, then:
• performing a write to the first copy of the mirrored dataset over the first path;
• polling the surrogate-capable node to determine whether the surrogate-capable node has a path having good status to the second storage node;
• if the surrogate-capable node has a path having good status to the second storage node, encapsulating a write request to the second copy and transmitting that encapsulated write request to the surrogate-capable node;
• and
• de-encapsulating the encapsulated write request to the second copy and forwarding it from the surrogate-capable node to the second storage node.