While removing one host from a multi-node cluster, when the Hadoop services are not running (i.e. Datanode is not in the started state )
I got the following error:
Component data node on host vmforkaran.informatica.com cannot be decommissioned as it's not in STARTED state
Yes, the DataNode must be running when we try to enable the Decommission for that DataNode.
This is needed because when an administrator decommission a datanode, the datanode will first be transitioned into DECOMMISSION_INPROGRESS state. After all blocks belonging to that datanode have been fully replicated elsewhere based on each block’s replication factor. the datanode will be transitioned to DECOMMISSIONED state. After that, the administrator can shutdown the node.
You can check the DataNode status like Decommissioned...etc in NameNode UI in the mean time.
Additionally please refer to the following link which explains the sequence of Removing a Node (Host) from multinode cluster.
You must decommission a master or slave running on a host before removing it or its host from service. Decommissioning helps you to prevent potential loss of data or disruption of service. Decommissioning is available for the following component types:
Decommissioning executes the following tasks: