Configure ViewFs

Configure ViewFs to create common views for file and directory paths corresponding to locations on different NameNodes of a federated HDFS cluster by specifying mount table entries. You can use Ambari Web UI to specify ViewFs as the default file system, and specify mount table entries for the file and directory paths.

1. In Ambari Web, select Services > HDFS > Configs, and navigate to Advanced core-site.
2. Update the value of the fs.defaultFS property to viewfs://<clustername>.
   For example, if your cluster is named Clusterx, set the value to viewfs://ClusterX.

   This sets ViewFs as the default file system.

   	Note
   	Updating fs.defaultFS to ViewFs also updates the default root to point to the ViewFs root. Therefore, you must remap any directory paths mounted earlier to point to the namespaces that contain those directories.

3. Use either of the following options to specify the mount table entries for the file and directory paths.
   Key-value pairs in core-site.xml:

   1. Navigate to Custom core-site.
   2. Click Add property.
   3. Add a path name property as the key, its corresponding mount point as the value, and click Add.

      Add similar key-value pairs for all the file and directory paths you want to mount.

      For example, if ClusterX has a directory named /tmp in the namespace ns1 and another directory named /foo in the namespace ns2, you can define the following key-value pairs:

      Key	Value
      fs.viewfs.mounttable.ClusterX.link./tmp	hdfs://ns1/tmp
      fs.viewfs.mounttable.ClusterX.link./foo	hdfs://ns2/foo

   4. Click Save.
   5. Add a description of the configuration changes, and click Save.
   6. Restart HDFS and other services as applicable.
   Mount table configuration file:

   1. Navigate to Advanced viewfs-mount-table.
   2. Enter the mount table entries to the various file and directory paths as properties in the text box.
      For the previous example, you can specify mount table entries for the directories /foo and /tmp as follows:

      <configuration>
        <property>
          <name>fs.viewfs.mounttable.ClusterX.link./tmp</name>
          <value>hdfs://ns1/tmp</value>
        </property>
        <property>
          <name>fs.viewfs.mounttable.ClusterX.link./foo</name>
          <value>hdfs://ns2/foo</value>
        </property>
      </configuration>
      

   3. Click Save.
   4. Add a description of the configuration changes, and click Save.
   5. Restart HDFS and other services as applicable.