anchor.diff:  build_delta_recovery_buckets_loop_test() ->
       MappedConfigs = [{"b1", conf1, {map, opts}},
                        {"b2", conf2, false}],
  -    [] = build_delta_recovery_buckets_loop([], all, []),
  -    [] = build_delta_recovery_buckets_loop(MappedConfigs, all, []),
  -    [] = build_delta_recovery_buckets_loop(MappedConfigs, ["b2"], []),
  -    [] = build_delta_recovery_buckets_loop(MappedConfigs, ["b1", "b2"], []),
  -    [] = build_delta_recovery_buckets_loop(MappedConfigs, [], []),
  -    ?assertEqual([{"b1", conf1, {map, opts}}], build_delta_recovery_buckets_loop(MappedConfigs, ["b1"], [])),
  -    ?assertEqual([{"b1", conf1, {map, opts}}], build_delta_recovery_buckets_loop([hd(MappedConfigs)], all, [])).
  +    {ok, []} = build_delta_recovery_buckets_loop([], all, []),
  +    {error, not_possible} = build_delta_recovery_buckets_loop(MappedConfigs, all, []),
  +    {error, not_possible} = build_delta_recovery_buckets_loop(MappedConfigs, ["b2"], []),
  +    {error, not_possible} = build_delta_recovery_buckets_loop(MappedConfigs, ["b1", "b2"], []),
  +    {ok, []} = build_delta_recovery_buckets_loop(MappedConfigs, [], []),
  +    ?assertEqual({ok, [{"b1", conf1, {map, opts}}]},
  +                 build_delta_recovery_buckets_loop(MappedConfigs, ["b1"], [])),
  +    ?assertEqual({ok, [{"b1", conf1, {map, opts}}]},
  +                 build_delta_recovery_buckets_loop([hd(MappedConfigs)], all, [])).
   
   apply_delta_recovery_buckets([], _DeltaNodes, _CurrentBuckets) ->
       ok;
  
positive.code:     end.
  
  build_delta_recovery_buckets(_AllNodes, [] = _DeltaNodes, _AllBucketConfigs, _DeltaRecoveryBuckets) ->
      [];
  build_delta_recovery_buckets(AllNodes, DeltaNodes, AllBucketConfigs, DeltaRecoveryBuckets) ->
      Config = ns_config:get(),
  
  
negative.code: 
                         rebalance(KeepNodes, EjectNodes, FailedNodes,
                                   BucketConfigs,
                                   DeltaNodes, DeltaRecoveryBucketTuples);
                     {error, not_possible} ->
                         proc_lib:init_ack({error, delta_recovery_not_possible})
                 end
         end, []]).
  
  