prometheus.NewDesc(
			prometheus.BuildFQName(minioNamespace, "capacity_usable", "total"),
			"Total usable capacity online in the cluster",
			nil, nil),
		prometheus.GaugeValue,
		float64(GetTotalUsableCapacity(server.Disks, sinfo)),
	)

	// Report total usable capacity free
	ch <- prometheus.MustNewConstMetric(
		prometheus.NewDesc(
			prometheus.BuildFQName(minioNamespace, "capacity_usable_free", "total"),

	}
	if idx+1 > len(z.serverPools) {
		return pi, errInvalidArgument
	}

	info := z.serverPools[idx].StorageInfo(context.Background())
	info.Backend = z.BackendInfo()

	usableTotal := int64(GetTotalUsableCapacity(info.Disks, info))
	usableFree := int64(GetTotalUsableCapacityFree(info.Disks, info))
	return poolSpaceInfo{
		Total: usableTotal,
		Free:  usableFree,
		Used:  usableTotal - usableFree,
	}, nil