# Running and stopping Data Optimizer in Cloudera Use the following best practices when starting or stopping Data Optimizer, its volumes, and other services in Cloudera. ## Start and stop Data Optimizer When you are stopping services for a single host or for all hosts in the cluster, as a best practice, always start the Data Optimizer volume component before the HDFS DataNode component and stop it after the HDFS DataNode component. Stopping the Data Optimizer volume while HDFS is running might lead to data availability issues or lead to transient HDFS volume failures. Starting HDFS when Data Optimizer is not running can negatively impact your operations. If the DataNode is not put into maintenance mode, more blocks will be created to maintain the number of required replication copies. As a best practice, set the DataNode to a maintenance state as described in [HDFS-7877](https://issues.apache.org/jira/browse/HDFS-7877) to avoid unnecessarily re-protecting a large number of blocks on a Data Optimizer volume when performing routine DataNode maintenance. ## Start and stop Data Optimizer volumes As a best practice, always start Data Optimizer volumes before the HDFS DataNodes and stop them after stopping the HDFS DataNodes. This sequence ensures optimal operation and prevents potential data availability issues. Like most services and service roles, the Data Optimizer service and the Volume role include `start` and `stop` commands that you can access and execute in multiple ways through Cloudera Manager. * **Service-wide actions** Use the **Start** and **Stop** actions on the Data Optimizer service to start and stop all volume instances associated with the service simultaneously. * **Individual volume actions** Start and stop individual volume instances through the Hosts tab. Drill down into an individual host and select Start, Stop, or Restart from the action menu for the specific volume instance. ## Start and stop all services Cloudera Manager does not provide a way to define dependencies between services or to influence the order when stopping or starting all services or when performing rolling restarts. Cloudera Manager is unaware that HDFS depends on Data Optimizer and assumes that Data Optimizer (like most services) is dependent on HDFS. Because of this, when using the cluster or host level `Start`, `Stop`, and `Restart` commands, HDFS will be stopped after Data Optimizer, and started before Data Optimizer, which is not recommended. Be aware that the cluster `Stop` command stops Data Optimizer volumes before it stops HDFS DataNodes. The cluster **Start** command starts HDFS DataNodes before it starts Data Optimizer volumes. For this reason, always start the Data Optimizer service before using the cluster `Start` command. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.pentaho.com/pdc-10.2-data-optimizer/pdso-install-landing-page/pdso-install-in-hadoop-cluster/pdso-run-data-optimizer-landing-page/running-and-stopping-data-storage-optimizer-cp/running-and-stopping-data-storage-optimizer-in-cloudera.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.