public int getNumberOfLeafGroups() {
        if (subgroups.isEmpty()) return 1;
        int count = 0;
        for (StorageGroup g : subgroups)
            count += g.getNumberOfLeafGroups();
        return count;
    }
Returns all the nodes below this group
config-model/src/main/java/com/yahoo/vespa/model/content/StorageGroup.java