今天在学hadoop Shell客户端启动，在往hdfs原有文件中追加文件发现以下问题：
1）：如果集群中的文件是空文件，则能追加进去。
2）：如果集群中的文件有内容，则追加的时候会报错。
java.io.IOException: Failed to replace a bad datanode on the existing pipeline due to no more good datanodes being available to try. (Nodes: current=[DatanodeInfoWithStorage[192.168.59.13:50010,DS-7feab941-bbe9-4760-8459-08894ff8bdbe,DISK], DatanodeInfoWithStorage[192.168.59.14:50010,DS-c43301df-a9f0-4801-b985-6f0cad6f03b5,DISK]], original=[DatanodeInfoWithStorage[192.168.59.13:50010,DS-7feab941-bbe9-4760-8459-08894ff8bdbe,DISK], DatanodeInfoWithStorage[192.168.59.14:50010,DS-c43301df-a9f0-4801-b985-6f0cad6f03b5,DISK]]). The current failed datanode replacement policy is DEFAULT, and a client may configure this via 'dfs.client.block.write.replace-datanode-on-failure.policy' in its configuration.
at org.apache.hadoop.hdfs.DataStreamer.findNewDatanode(DataStreamer.java:1281)
at org.apache.hadoop.hdfs.DataStreamer.addDatanode2ExistingPipeline(DataStreamer.java:1353)
at org.apache.hadoop.hdfs.DataStreamer.handleDatanodeReplacement(DataStreamer.java:1568)
at org.apache.hadoop.hdfs.DataStreamer.setupPipelineForAppendOrRecovery(DataStreamer.java:1469)
at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:708)

查阅资料发现，往空文件中追加就相当于直接写文件，所以能追加进去，而往有内容的文件中追加不进去是因为datanode节点数不够三个，再克隆一台虚拟机，加到hdfs集群中就能解决问题。