code: private boolean addStoredBlock(Block block,
                                 DatanodeDescriptor node,
                                 DatanodeDescriptor delNodeHint) throws IOException {
      return addStoredBlockInternal(block, node, delNodeHint, false, null);
    }
docs: Modify (block-->datanode) map. Remove block from set of needed replications
  if this takes care of the problem.
  
  @return whether or not the block was stored.
  @throws IOException