Return allocated size (fraction of total snapshot volume space). If this is not a snapshot volume,
		than RuntimeError exception is raised.

		:return: float

def snapshot_allocation(self):
		""" Return allocated size (fraction of total snapshot volume space). If this is not a snapshot volume,
		than RuntimeError exception is raised.

		:return: float
		"""
		check_cmd = ['lvs', self.volume_path(), '-o', 'snap_percent', '--noheadings']
		output = subprocess.check_output(check_cmd, timeout=self.__class__.__lvm_snapshot_check_cmd_timeout__)
		output = output.decode().strip()
		if len(output) == 0:
			raise RuntimeError('Unable to check general logical volume')
		return float(output.replace(',', '.', 1))