public static function storageInstance() {
		if (self::$instance) {
			return self::$instance;
		}

		if (!isset(self::$registry[self::driver()])) {
			throw new StorageException("Invalid driver '".self::driver()."'");
		}

		$class = self::$registry[self::driver()];
		self::$instance = new $class();

		return self::$instance;
	}