def update_volumes(cls, instance):
        attrs = instance.attributes
        if not attrs:
            attrs = cls.create_attributes(instance)

        try:
            attrs.volumes = instance.volume_manager.gen_volumes_info()
        except Exception as exc:
            msg = (
                u"Failed to generate volumes "
                u"info for node '{0}': '{1}'"
            ).format(
                instance.name or instance.mac or instance.id,
                str(exc) or "see logs for details"
            )
            logger.warning(traceback.format_exc())
            Notification.create({
                "topic": "error",
                "message": msg,
                "node_id": instance.id
            })

        if instance.cluster_id:
            Cluster.add_pending_changes(
                instance.cluster,
                "disks",
                node_id=instance.id
            )

        db().add(attrs)
        db().flush()

 def set_error_status_and_file_notification(cls, instance, etype, emessage):
     instance.status = consts.NODE_STATUSES.error
     instance.error_type = etype
     instance.error_msg = emessage
     db().flush()
     Notification.create(
         {"topic": consts.NOTIFICATION_TOPICS.error, "message": instance.error_msg, "node_id": instance.id}
     )

    def set_default_node_volumes(cls, node):
        from .objects.volumes import VolumeObject

        try:
            VolumeObject.set_default_node_volumes(node)
        except Exception as exc:
            logger.exception(exc)
            msg = "Failed to generate volumes for node '{0}': '{1}'".format(
                node.human_readable_name, six.text_type(exc)
            )
            Notification.create({"topic": "error", "message": msg, "node_id": node.id})

        if node.cluster_id:
            Node.add_pending_change(node, "disks")

    def update_volumes(cls, instance):
        """Update volumes for Node instance.
        Adds pending "disks" changes for Cluster which Node belongs to

        :param instance: Node instance
        :returns: None
        """
        attrs = instance.attributes
        if not attrs:
            attrs = cls.create_attributes(instance)

        try:
            # TODO(eli): update volumes method should be moved
            # into an extension
            # Should be done as a part of blueprint:
            # https://blueprints.launchpad.net/fuel/+spec
            #                                 /volume-manager-refactoring
            from nailgun.extensions.volume_manager.extension \
                import VolumeManagerExtension
            VolumeManagerExtension.set_volumes(
                instance,
                instance.volume_manager.gen_volumes_info())
        except Exception as exc:
            msg = (
                u"Failed to generate volumes "
                u"info for node '{0}': '{1}'"
            ).format(
                instance.name or instance.mac or instance.id,
                str(exc) or "see logs for details"
            )
            logger.warning(traceback.format_exc())
            Notification.create({
                "topic": "error",
                "message": msg,
                "node_id": instance.id
            })

        if instance.cluster_id:
            Cluster.add_pending_changes(
                instance.cluster,
                "disks",
                node_id=instance.id
            )

        db().add(attrs)
        db().flush()

    def create_discover_notification(cls, instance):
        """Create notification about discovering new Node

        :param instance: Node instance
        :returns: None
        """
        try:
            # we use multiplier of 1024 because there are no problems here
            # with unfair size calculation
            ram = str(round(float(
                instance.meta['memory']['total']) / 1073741824, 1)) + " GB RAM"
        except Exception:
            logger.warning(traceback.format_exc())
            ram = "unknown RAM"

        try:
            # we use multiplier of 1000 because disk vendors specify HDD size
            # in terms of decimal capacity. Sources:
            # http://knowledge.seagate.com/articles/en_US/FAQ/172191en
            # http://physics.nist.gov/cuu/Units/binary.html
            hd_size = round(
                float(
                    sum(
                        [d["size"] for d in instance.meta["disks"]]
                    ) / 1000000000
                ),
                1
            )
            # if HDD > 100 GB we show it's size in TB
            if hd_size > 100:
                hd_size = str(hd_size / 1000) + " TB HDD"
            else:
                hd_size = str(hd_size) + " GB HDD"
        except Exception:
            logger.warning(traceback.format_exc())
            hd_size = "unknown HDD"

        cores = str(instance.meta.get('cpu', {}).get('total', "unknown"))

        Notification.create({
            "topic": "discover",
            "message": u"New node is discovered: "
                       u"{0} CPUs / {1} / {2} ".format(cores, ram, hd_size),
            "node_id": instance.id
        })