Decommissioning is a process that supports removing a slave component from the cluster. You must decommission the slave running on a host before removing the component or host from service to avoid potential loss of data or disruption on processing. Decommissioning is available for the following component types:
DataNodes
NodeManagers
TaskTrackers
RegionServers
Decommissioning executes the following steps:
For DataNodes, safely replicates the HDFS data to other DataNodes in the cluster.
For NodeManagers and TaskTrackers, stops accepting new job requests from the masters and stops the component.
For RegionServers, turns on drain mode and stops the component.
To initiate a decommission, browse the host details page and select the Decommission option from the Actions menu next to the component you want to decommission. The UI shows "Decommissioning" status while steps process, then "Decommissioned" when complete.
For example, to move a DataNode slave from one host to another, decommission the DataNode.
