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):

　　dfs.balance.bandwidthPerSec

　　1048576

　　　　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)