secondarynamenode的作用就是用来做checkpoint---相当于对NameNode节点的元数据备份

现在将secondarynamenode部署在另一台机器，是为了引入Zookeeper做自动切换

具体方法如下

1.修改conf/core-site.xml

增加或修改

<property>

<name>fs.checkpoint.period</name>

<value>3600</value>

<description>The number of seconds between two periodic checkpoints. </description>

</property>

<property>

<name>fs.checkpoint.size</name>

<value>67108864</value>

<description>The size of the current edit log (in bytes) that triggers a periodic checkpoint even if the fs.checkpoint.period hasn't expired. </description>

</property>

<property>

<name>fs.checkpoint.dir</name>  --可以不写，默认为 {hadoopdata}/dfs/namesecondary

<value>/data/work/hdfs/namesecondary</value>

<description>Determines where on the local filesystem the DFS secondary name node should store the temporary images to merge. If this is a comma-delimited list of directories then the image is replicated in all of the directories for redundancy. </description>

</property>

 

2.修改conf/hdfs-site.xml

<property>

<name>dfs.http.address</name>

 <value>0.0.0.0:50070</value>

<description> The address and the base port where the dfs namenode web ui will listen on. If the port is 0 then the server will start on a free port. </description>

</property>

0.0.0.0改为namenode的IP地址（Master的IP）

 

3.修改conf/masters

  将secondarynamenode的机器IP写入，可以多写，一行一个IP

 

4.重启HADOOP，检查secondarynamenode是否已启动 

在Master节点上输入 jps 可以看到    NameNode,Jobtracker

在DataNode上输入jps可以看到        DataNode,Tasktracker

在secondarynamenode上输入jps可以看到   Secondarynamenode 

进入secondarynamenode的目录/data/work/hdfs/namesecondary

正确的结果：

如果没有，请耐心等待，只有到了设置的checkpoint的时间或者大小，才会生成。