Method for reliably updating a data group in a read-before-write data replication environment using a comparison file

A method for reliably updating a data group in a read-before-write replication environment, the method performed by executable code stored on a non-transitory storage device and executed by a processor and comprising:

• receiving at a storage controller separate from a first non-volatile storage medium an updated data group sent from the first nonvolatile storage medium in a read-before-write operation, wherein the updated data group comprises unchanged data values and updated data values to replace previous data values:
• copying a previous data group stored on a second non-volatile storage medium into a controller memory of the storage controller;
• comparing the updated data group with the previous data group using an Exclusive OR (XOR) command;
• storing results of the comparison of the updated data group and the previous data group as a comparison file, the comparison file comprising the differences between updated data values in the updated data group and the previous data values in the previous data group;
• compressing the comparison file;
• informing a peer controller prior to writing the updated data group to the second nonvolatile storage medium, the peer controller configured to complete the read-before write operation for the storage controller in case of failure;
• communicating the comparison file and the updated data group to the peer controller;
• synchronizing the updated data group to the peer controller;
• writing the updated data group to the second non-volatile storage medium;
• informing the peer controller that the updated data group is written to the second non-volatile storage medium;
• discarding the updated data group from the peer controller upon being informed that the updated data group was successfully written to the second non-volatile storage medium;
• detecting a system failure;
• reading the updated data group from the second non-volatile storage medium and the comparison file into the controller memory;
• recovering the previous data group from the updated data group and the comparison file using an XOR command;
• and
• writing the recovered previous data group to the second non-volatile storage medium. 14.