@staticmethod
def fixed_pattern(pattern=None, io_size='8k'):
    """ renew the fixed pattern

        generate a data with fixed data pattern 
        :return : data pattern in bytes
        """
    iosize = int(io_size)
    tmpbytes = bytes('content of data pattern is not important', encoding=
        'utf-8')
    if pattern is not None:
        tmpbytes = bytes(tmpbytes, encoding='utf-8')
    if len(tmpbytes) >= iosize:
        return tmpbytes[:iosize]
    else:
        number = iosize // len(tmpbytes)
        remainder = tmpbytes[:iosize % len(tmpbytes)]
        return tmpbytes * number + remainder
