NameNode:
<property>
<name>dfs.name.dir</name>
<value>/home/hadoop/dfs/name,/mnt/hadoop-backup</value>
<fi nal>true</fi nal>
</property>
/mnt/hadoop-backup 是SSN在NameNode的挂载点,NameNode同时将metadata写入/home/hadoop/dfs/name,/mnt/hadoop-backup中
当一个namenode失败的时候,you should moving the IP address, setting up a new backup node