def get_persistent_boot_device(self):
        """Get current persistent boot device set for the host

        :returns: persistent boot device for the system
        :raises: IloError, on an error from iLO.
        """
        sushy_system = self._get_sushy_system(PROLIANT_SYSTEM_ID)
        # Return boot device if it is persistent.
        if ((sushy_system.
             boot.enabled) == sushy.BOOT_SOURCE_ENABLED_CONTINUOUS):
            return PERSISTENT_BOOT_MAP.get(sushy_system.boot.target)
        # Check if we are in BIOS boot mode.
        # There is no resource to fetch boot device order for BIOS boot mode
        if not self._is_boot_mode_uefi():
            return None

        try:
            boot_device = (sushy_system.bios_settings.boot_settings.
                           get_persistent_boot_device())
            return PERSISTENT_BOOT_MAP.get(boot_device)
        except sushy.exceptions.SushyError as e:
            msg = (self._("The Redfish controller is unable to get "
                          "persistent boot device. Error %(error)s") %
                   {'error': str(e)})
            LOG.debug(msg)
            raise exception.IloError(msg)
Get current persistent boot device set for the host

        :returns: persistent boot device for the system
        :raises: IloError, on an error from iLO.