anchor.diff:                      lager:info("GC: discarding replica of ~p on ~p/~p",
                                  [BlobName, Node, Vol]),
                       {ok, true};
  -                {false, false}
  +                {false, false, false}
                     when BlackList =:= [] ->
                       % This is a usable, newly-recovered, lost replica;
                       % record the volume for later use.
  
positive.code:     DiskUsage = avg_disk_usage(NodeStats),
      OverusedNodes = find_unstable_nodes(overused, NodeStats, DiskUsage),
      UnderusedNodes = find_unstable_nodes(underused, NodeStats, DiskUsage),
      lager:info("GC: average disk utilization: ~p, "
                 "over utilized nodes: ~p, "
                 "under utilized nodes: ~p",
  
negative.code:                     NewRecovered = [{Node, Vol} | Recovered],
                      ets:update_element(gc_blobs, BlobName, {3, NewRecovered}),
                      {ok, false};
                  {false, false, false} ->
                      {RepNodes, _RepVols} = lists:unzip(Recovered),
                      Usable = find_usable(BlackList, lists:usort(RepNodes ++ PresentNodes)),
                      case length(Usable) > MaxReps of
  