Nodes normally run both a DataNode and a NodeManager, and both are typically commissioned or decommissioned together.
With the replication level set to three, HDFS is resilient to individual DataNodes failures. However, there is a high chance of data loss when you terminate DataNodes without decommissioning them first. Nodes must be decommissioned on a schedule that permits replication of blocks being decommissioned.
On the other hand, if a NodeManager is shut down, the ResourceManager will reschedule the tasks on other nodes in the cluster. However, decommissioning a NodeManager may be required in situations where you want a NodeManager to stop to accepting new tasks, or when the tasks take time to execute but you still want to be agile in your cluster management.
