Here is the sample command output ran on the datanode
[hdfs@xxxx ~]$ hdfs dfsadmin -triggerBlockReport xxxx.openstacklocal:8010Triggering a full block report on xxxx.openstacklocal:8010.
6. Open the NN UI again and now will see Under Replicated blocks
Which will be decreasing as the data gets replicated
7. We need to wait until the Under replicated blocks turn to 0.
8. Once the Under Replicated block becomes 0, we need to iterate Step1-7 for Second DN and so on for all the DNs.
9. Once all the DNs started and the NN UI is back to healthy state (i.e. no missing, corrupt or under-replicated blocks), It is safe to re-start the NN
10. Verify the NN UI again to double check the health status of NN after restart.
11. If all good, it’s safe to restart other services which require restart.