Time for action – adding an additional fsimage location

Let's now configure our NameNode to simultaneously write multiple copies of fsimage to give us our desired data resilience. To do this, we require an NFS-exported directory.

1. Ensure the cluster is stopped.

   $ stopall.sh
   

2. Add the following property to Hadoop/conf/core-site.xml, modifying the second path to point to an NFS-mounted location to which the additional copy of NameNode data can be written.

   <property>
   <name>dfs.name.dir</name>
   <value>${hadoop.tmp.dir}/dfs/name,/share/backup/namenode</value>
   </property>

3. Delete any existing contents of the newly added directory.

   $ rm -f /share/backup/namenode
   

4. Start the cluster.

   $ start-all.sh
   

5. Verify that fsimage is being written to both the specified locations by running the md5sum command against the two files specified before (change the following code depending on your configured locations):

   $ md5sum /var/hadoop/dfs/name/image/fsimage
   a25432981b0ecd6b70da647e9b94304a...