type nodesOnline struct {
	Online, Offline int
}

func newNodesUpDownCache() *cachevalue.Cache[nodesOnline] {
	loadNodesUpDown := func() (v nodesOnline, err error) {
		v.Online, v.Offline = globalNotificationSys.GetPeerOnlineCount()
		return
	}
	return cachevalue.NewFromFunc(1*time.Minute,
		cachevalue.Opts{ReturnLastGood: true},
		loadNodesUpDown)
}

type driveIOStatMetrics struct {
	readsPerSec    float64

	if len(peerClients) == 0 {
		return nil
	}
	idx := xxhash.Sum64String(s) % uint64(len(peerClients))
	return peerClients[idx]
}

// GetPeerOnlineCount gets the count of online and offline nodes.
func (sys *NotificationSys) GetPeerOnlineCount() (nodesOnline, nodesOffline int) {
	nodesOnline = 1 // Self is always online.
	nodesOffline = 0
	nodesOnlineIndex := make([]bool, len(sys.peerClients))

	networkMetricsPrometheus(ch)
	httpMetricsPrometheus(ch)
	healingMetricsPrometheus(ch)
}

func nodeHealthMetricsPrometheus(ch chan<- prometheus.Metric) {
	nodesUp, nodesDown := globalNotificationSys.GetPeerOnlineCount()
	ch <- prometheus.MustNewConstMetric(
		prometheus.NewDesc(
			prometheus.BuildFQName(minioNamespace, "nodes", "online"),
			"Total number of MinIO nodes online",
			nil, nil),
		prometheus.GaugeValue,

		metricsGroupOpts: opts,
	}
	mg.RegisterRead(func(_ context.Context) (metrics []MetricV2) {
		metrics = make([]MetricV2, 0, 16)
		nodesUp, nodesDown := globalNotificationSys.GetPeerOnlineCount()
		metrics = append(metrics, MetricV2{
			Description: getNodeOnlineTotalMD(),
			Value:       float64(nodesUp),
		})
		metrics = append(metrics, MetricV2{
			Description: getNodeOfflineTotalMD(),