Return chunk no and 1-based offset of key
        :param key:
        :return:

def _get_key_location(self, key) -> (int, int):
        """
        Return chunk no and 1-based offset of key
        :param key:
        :return:
        """
        key = int(key)
        if key == 0:
            return 1, 0
        remainder = key % self.chunkSize
        addend = ChunkedFileStore.firstChunkIndex
        chunk_no = key - remainder + addend if remainder \
            else key - self.chunkSize + addend
        offset = remainder or self.chunkSize
        return chunk_no, offset