'Returns the size of the data on disk'

def get_size(self, nice_size=False):

    if self.file_size:
        if nice_size:
            return galaxy.util.nice_size(self.file_size)
        else:
            return self.file_size
    elif nice_size:
        return galaxy.util.nice_size(self._calculate_size())
    else:
        return self._calculate_size()
