A method for modifying a file having a file size exceeding a size of available main memory, the file arranged in one or more existing data blocks, by writing an array of new data to the file at a file offset to replace a portion of the existing data of the file. The method including determining one or more target data blocks of the file which contain data to be replaced, considering a size of the array of new data, the block size of the file and the file offset within the file, retrieving at least one of the target data blocks from the file, creating at least one new data block comprised of at least one of the one or more write byte arrays, and writing the new data block to the file at the location of the target data blocks.