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

		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(),