code: boolean isReplicaCorrupt(Block blk, DatanodeDescriptor node) {
      Collection<DatanodeDescriptor> nodes = getNodes(blk);
      return ((nodes != null) && (nodes.contains(node)));
    }
docs: Check if replica belonging to Datanode is corrupt
  
  @param blk Block to check
  @param node DatanodeDescriptor which holds the replica
  @return true if replica is corrupt, false if does not exists in this map