private void validateThatGroupSiblingsAreUnique(String cluster, StorageGroup group) {
            if (group == null) return; // Unit testing case

            validateGroupSiblings(cluster, group);
            for (StorageGroup g : group.getSubgroups()) {
                validateThatGroupSiblingsAreUnique(cluster, g);
            }
        }
Returns of memory reserved on a host. Memory is reserved for the jvm if the cluster is combined
config-model/src/main/java/com/yahoo/vespa/model/content/cluster/ContentCluster.java