interfaceRxBytes  MetricName = "rx_bytes"
	interfaceRxErrors MetricName = "rx_errors"
	interfaceTxBytes  MetricName = "tx_bytes"
	interfaceTxErrors MetricName = "tx_errors"

	// cpu stats
	cpuUser       MetricName = "user"
	cpuSystem     MetricName = "system"
	cpuIOWait     MetricName = "iowait"
	cpuIdle       MetricName = "idle"
	cpuNice       MetricName = "nice"
	cpuSteal      MetricName = "steal"
	cpuLoad1      MetricName = "load1"

// value of this type is passed to the `MetricsLoaderFn`.
type MetricValues struct {
	values      map[MetricName][]metricValue
	descriptors map[MetricName]MetricDescriptor
}

func newMetricValues(d map[MetricName]MetricDescriptor) MetricValues {
	return MetricValues{
		values:      make(map[MetricName][]metricValue, len(d)),
		descriptors: d,
	}
}

	freeBytes       MetricName = "free_bytes"
	readBytes       MetricName = "read_bytes"
	rcharBytes      MetricName = "rchar_bytes"
	receivedBytes   MetricName = "received_bytes"
	latencyMilliSec MetricName = "latency_ms"
	sentBytes       MetricName = "sent_bytes"
	totalBytes      MetricName = "total_bytes"
	usedBytes       MetricName = "used_bytes"

			for k, v := range v.Failed.ErrCounts {
				v2.Failed.ErrCounts[k] += v
			}
			if v2.XferStats == nil {
				v2.XferStats = make(map[replication.MetricName]replication.XferStats)
			}
			for rm, x := range v.XferStats {
				x2, ok := v2.XferStats[replication.MetricName(rm)]
				if !ok {
					x2 = replication.XferStats{}
				}
				x2.AvgRate += x.Avg
				x2.CurrRate += x.Curr
				if x.Peak > x2.PeakRate {