NameNodes maintain the namespace tree for HDFS and a mapping of file blocks to DataNodes where the data is stored. A simple HDFS cluster can have only one primary NameNode, supported by a secondary NameNode that periodically compresses the NameNode edits log file that contains a list of HDFS metadata modifications. This reduces the amount of disk space consumed by the log file on the NameNode, which also reduces the restart time for the primary NameNode. A high availability cluster contains two NameNodes: active and standby.
Formatting the NameNode and Creating the /tmp Directory
Minimum Required Role: Cluster Administrator (also provided by Full Administrator)
When you add an HDFS service, the wizard automatically formats the NameNode and creates the /tmp directory on HDFS. If you quit the wizard or it does not finish, you can format the NameNode and create the /tmp directory outside the wizard by doing these steps:
- Stop the HDFS service if it is running. See Starting, Stopping, and Restarting Services.
- Click the Instances tab.
- Click the NameNode role instance.
- Select .
- Start the HDFS service.
- Select .