Systems and methods for cache synchronization between redundant storage controllers

A system comprising:

• a first storage controller having a cache memory;
• a second storage controller having a mirrored cache memory;
• and
• a communication channel coupling the first controller and the peer controller for exchanging cache coherency information,
• wherein the first controller further comprises:
• a filling buffer list for accumulating header information regarding changes in the cache memory of the first controller;
• an active buffer list for transmitting previously accumulated header information regarding changes in the cache memory of the first controller from the first controller to the peer controller;
• and
• a first coherency element coupled to the filling buffer list and coupled to the active buffer list to generate header information regarding changes in the cache memory of the first controller resulting from performing read and write operations and to store the generated header information in the filling buffer and to transmit the active buffer to the peer controller,
• wherein the second controller further comprises:
• a second coherency element for receiving the transmitted header information from the first coherency element to update the mirrored cache memory accordingly, and
• wherein the first controller forwards no cache data to the second controller in response to periodic cache flush operations performed by the first controller.

A method for maintaining cache coherency between a cache memory in a first controller and a mirror cache memory in a peer controller, the method comprising the steps of:

• generating in the first controller update meta-data regarding dirty data in the cache memory of the first controller altered in response to write requests received from an attached host system;
• generating in the first controller invalidation meta-data regarding dirty data in the cache memory of the first controller flushed by the first controller in response to read or write requests received from an attached host system;
• periodically transmitting the generated meta-data and any corresponding dirty data from the first controller to the peer controller to permit the peer controller to update its mirrored cache memory in accordance with the received meta-data and any corresponding cache data,
• wherein the steps of generating each include generating meta-data into a currently filling buffer as a previously filled buffer is being transmitted and wherein the step of periodically transmitting includes the step of swapping the currently filling buffer and previously filled buffer after completion of the transmission of the previously filled buffer.

A system for maintaining cache coherency between a first controller and a peer controller, the system comprising:

• updating means for updating cache data in a write-back cache memory in the first controller in response to read or write requests from an attached host;
• buffering means for buffering information regarding changes to the cache memory m the first controller that affect cache coherency of a mirrored cache memory in the peer controller;
• and
• transmitting means for transmitting the buffered information and associated cache data from the first controller to the peer controller to maintain cache coherency between the cache memory of the first controller and that mirrored cache memory of the peer controller,
• wherein the buffered information serves to maintain cache coherency without requiring a step of informing the peer controller of any cache flush operation performed in the first controller, and
• wherein the buffering means further comprises:
• means for filling a first buffer while a second buffer is transmitting to the peer controller;
• means for sensing completion of transmission of the second buffer to the peer controller;
• and
• means for filling the second buffer while the first buffer is transmitting to the peer controller.