public int countNodes(boolean includeRetired) {
        int nodeCount = (int)nodes.stream().filter(node -> includeRetired || ! node.isRetired()).count();
        for (StorageGroup group : subgroups)
            nodeCount += group.countNodes(includeRetired);
        return nodeCount;
    }
Returns the total number of nodes below this group
config-model/src/main/java/com/yahoo/vespa/model/content/StorageGroup.java