def add_raw_data(self, data, attrs):
        """ Add raw data for a read.

        :param data: The raw data DAQ values (16 bit integers).

        The read must already exist in the file. It must not already
        have raw data.
        """
        self.assert_writeable()
        if "Raw" not in self.handle:
            self.handle.create_group("Raw")
        if "Signal" in self.handle['Raw']:
            msg = "Fast5 file already has raw data for read '{}' in: {}"
            raise KeyError(msg.format(self.read_id, self.filename))
        self.handle['Raw'].create_dataset('Signal', data=data, compression='gzip', shuffle=True, dtype='i2')
        self._add_attributes("Raw", attrs, clear=True)
Add raw data for a read.

        :param data: The raw data DAQ values (16 bit integers).

        The read must already exist in the file. It must not already
        have raw data.