secondary namenoded 配置很容易被忽视，如果jps检查都正常，大家通常不会太关心，除非namenode发生问题的时候，才会想起还有个secondary namenode，它的配置共两步：
- 集群配置文件conf/master中添加secondarynamenode的机器
- 修改/添加 hdfs-site.xml中如下属性：
<property>
<name>dfs.http.address</name>
<value>{your_namenode_ip}: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>
这两项配置OK后，启动集群。进入secondary namenode 机器，检查fs.checkpoint.dir（core-site.xml文件，默认为${hadoop.tmp.dir}/dfs/namesecondary）目录同步状态是否和namenode一致的。
如果不配置第二项则，secondary namenode同步文件夹永远为空，这时查看secondary namenode的log显示错误为：
2011-06-09 11:06:41,430 INFO org.apache.hadoop.hdfs.server.common.Storage: Recovering storage directory /tmp/hadoop-hadoop/dfs/namesecondary from failed checkpoint. 2011-06-09 11:06:41,433 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: Exception in doCheckpoint: 2011-06-09 11:06:41,434 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:211) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:529) at java.net.Socket.connect(Socket.java:478) at sun.net.NetworkClient.doConnect(NetworkClient.java:163) at sun.net.www.http.HttpClient.openServer(HttpClient.java:394) at sun.net.www.http.HttpClient.openServer(HttpClient.java:529) at sun.net.www.http.HttpClient.<init>(HttpClient.java:233) at sun.net.www.http.HttpClient.New(HttpClient.java:306) at sun.net.www.http.HttpClient.New(HttpClient.java:323) at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:970) at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:911) at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:836) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1172) at org.apache.hadoop.hdfs.server.namenode.TransferFsImage.getFileClient(TransferFsImage.java:151) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.downloadCheckpointFiles(SecondaryNameNode.java:256) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.doCheckpoint(SecondaryNameNode.java:313) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.run(SecondaryNameNode.java:225) at java.lang.Thread.run(Thread.java:662)
可能用到的core-site.xml文件相关属性：
<property>
<name>fs.checkpoint.period</name>
<value>300</value>
<description>The number of seconds between two periodic checkpoints.
</description>
</property>
<property>
<name>fs.checkpoint.dir</name>
<value>${hadoop.tmp.dir}/dfs/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>