A method in a data storage device receiving data including a data block and main error correction coding (ECC) data for the data block. The data block includes a first sub-block of data and a second sub-block of data. The method also includes initiating an ECC operation to process the data block using the main ECC data. In response to the ECC operation indicating uncorrectable errors in the data block, first additional ECC data that is external to the data block is retrieved and a second ECC operation is initiated to process the first sub-block of data using the first additional ECC data.