long getResourceTotalRegisteredHostDiskCapacity(String resource) {
    return getAllInstancesForResource(resource).stream()
        .map(instanceNameToInstanceConfig::get)
        .mapToInt(instanceConfig -> instanceConfig.getInstanceCapacityMap().get(DISK_KEY))
        .sum();
  }
Callback method when this data node is becoming SEMI AUTO from FULL AUTO.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixClusterManager.java