// This is wire-incompatible with Hadoop 2.0.0-alpha due to HDFS-3721
      // because it changes the length of the packet header, and BlockReceiver
      // in that version did not support variable-length headers.
// This is wire-incompatible with Hadoop 2.0.0-alpha due to HDFS-3721
      // because it changes the length of the packet header, and BlockReceiver
      // in that version did not support variable-length headers. | PacketHeader.java