# Step 9: Restart data nodes in Apache Ambari

In the Apache Ambari dashboard, perform the following steps:

1. Navigate to the HDFS Summary page.
2. At the top of the page, select either **Restart**, **Restart DataNodes**, or **Service Actions**.
3. Select the configuration settings that are consistent with your normal best practices for data node rolling restarts in this environment.
4. Select **Only restart DataNodes with stale configs**.
5. Select **Trigger Rolling Restart**.

After the rolling restart is complete, the data nodes start tiering to Data Optimizer.

For help verifying that tiering is occurring, see [Tiering HDFS Blocks to Pentaho Data Optimizer](/pdc-10.2-data-optimizer/pdso-install-landing-page/pdso-install-in-hadoop-cluster/pdso-maintain-landing-page/troubleshoot-data-storage-optimizer-fs/tiering-hdfs-blocks-to-pdso.md).


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