Cloudera Docs

Synchronizing the contents of JournalNodes

You can synchronize the contents of the JournalNodes in your CDH cluster. Enabling this capability helps in maintaining consistency in the contents of all the JournalNodes across the cluster. For example, a JournalNode whose contents go out of synchronization can automatically copy the contents of the other JournalNodes in the cluster to ensure consistency.

The cluster on which you want to enable JournalNode synchronization must have High Availability enabled.
  1. Go to the HDFS service.
  2. Click the Instances tab.
  3. Click the link labeled NameNode (Active).
    The NameNode instance page displays.
  4. Go to the Process tab.
  5. Click the hdfs-site.xml link under hdfs/hdfs.sh ["namenode"] to open a read-only copy of the file in a separate browser window.
  6. Note the URI value set for JournalNodes in the various dfs.namenode.shared.edits.dir parameters.
    The URI value should be in the format: 
    qjournal://host1:port1;host2:port2;host3:port3/journalId
  7. Return to the HDFS service page and click the Configuration tab.
  8. Search for the HDFS Service Advanced Configuration Snippet (Safety Valve) for hdfs-site.xml configuration option.
  9. Add the key dfs.namenode.shared.edits.dir to the selected configuration option and provide the value noted in Step 6.
  10. Click Save Changes.
  11. Restart HDFS.