Hadoop删除节点（Decommissioning Nodes）

1.集群配置
   修改conf/hdfs-site.xml文件

<property>
  <name>dfs.hosts.exclude</name>
  <value>/data/soft/hadoop/conf/excludes</value>
  <description>Names a file that contains a list of hosts that are
  not permitted to connect to the namenode.  The full pathname of the
  file must be specified.  If the value is empty, no hosts are
  excluded.</description>
</property>

<property>
  <name>dfs.hosts.exclude</name>
  <value>/data/soft/hadoop/conf/excludes</value>
  <description>Names a file that contains a list of hosts that are
  not permitted to connect to the namenode.  The full pathname of the
  file must be specified.  If the value is empty, no hosts are
  excluded.</description>
</property>

2确定要下架的机器
dfs.hosts.exclude定义的文件内容为,每个需要下线的机器，一行一个。这个将阻止他们去连接Namenode。如：

slave-003
slave-004

slave-003
slave-004

3.强制重新加载配置

[root@master hadoop]# ./bin/hadoop dfsadmin  -refreshNodes

[root@master hadoop]# ./bin/hadoop dfsadmin  -refreshNodes

它会在后台进行Block块的移动

4.关闭节点
   等待刚刚的操作结束后，需要下架的机器就可以安全的关闭了。

[root@master hadoop]# ./bin/ hadoop dfsadmin -report

[root@master hadoop]# ./bin/ hadoop dfsadmin -report

   可以查看到现在集群上连接的节点

  正在执行Decommission，会显示：
 

Decommission Status : Decommission in progress

Decommission Status : Decommission in progress

  执行完毕后，会显示：
 

Decommission Status : Decommissioned

Decommission Status : Decommissioned

5.再次编辑excludes文件
一旦完成了机器下架，它们就可以从excludes文件移除了

登录要下架的机器，会发现DataNode进程没有了，但是TaskTracker依然存在，需要手工处理一下

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