第六步：修改namenode的配置文件
hadoop@namenode:~$ cd hadoop-1.2.1/conf
hadoop@namenode:~/hadoop-1.2.1/conf$ vim slaves
datanode1
datanode2
第七步：负载均衡
hadoop@namenode:~/hadoop-1.2.1/conf$ start-balancer.sh
Warning: $HADOOP_HOME is deprecated.
starting balancer, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-balancer-namenode.out
以下摘自其他博客
1）如果不balance，那么cluster会把新的数据都存放在新的node上，这样会降低Map Reduce的工作效率
2）threshold是平衡阈值，默认是10%，值越低各节点越平衡，但消耗时间也更长
/app/hadoop/bin/start-balancer.sh -threshold 0.1
3）在namenode的配置文件 hdfs-site.xml 可以加上balance的带宽(默认值就是1M):
Specifies the maximum amount of bandwidth that each datanode
can utilize for the balancing purpose in term of
the number of bytes per second.
第八步：测试是否有效
1.启动hadoop
hadoop@namenode:~/hadoop-1.2.1$ start-all.sh
Warning: $HADOOP_HOME is deprecated.
starting namenode, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-namenode-namenode.out
datanode2: starting datanode, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-datanode-datanode2.out
datanode1: starting datanode, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-datanode-datanode1.out
namenode: starting secondarynamenode, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-secondarynamenode-namenode.out
starting jobtracker, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-jobtracker-namenode.out
datanode2: starting tasktracker, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-tasktracker-datanode2.out
datanode1: starting tasktracker, logging to /home/hadoop/hadoop-1.2.1/libexec/../logs/hadoop-hadoop-tasktracker-datanode1.out
hadoop@namenode:~/hadoop-1.2.1$
2.错误
运行wordcount程序时出现错误
hadoop@namenode:~/hadoop-1.2.1$ hadoop jar hadoop-examples-1.2.1.jar wordcount in out
Warning: $HADOOP_HOME is deprecated.
14/09/12 08:40:39 ERROR security.UserGroupInformation: PriviledgedActionException as:hadoop cause:org.apache.hadoop.ipc.RemoteException: org.apache.hadoop.mapred.SafeModeException: JobTracker is in safe mode
at org.apache.hadoop.mapred.JobTracker.checkSafeMode(JobTracker.java:5188)
at org.apache.hadoop.mapred.JobTracker.getStagingAreaDir(JobTracker.java:3677)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:587)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1432)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1428)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.j