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Posts: 6
Registered: ‎12-05-2017

Role of 'prepare' command & 'safemode' in HDFS Rolling Upgrade

[ Edited ]

In HDFS rolling upgrade page at a high level I am seeing the steps mentioned like below


  1. hdfs dfsadmin -rollingUpgrade prepare
  2. Upgrade standby NN2 and start NN2 with hdfs dfsadmin -rollingUpgrade started
  3. Shutdown, upgrade NN1 and start NN1 with hdfs dfsadmin -rollingUpgrade started

But in cloudera documentation of Hadoop to prepare the cluster for upgrade it is just saying to enter NN in safemode & save namespace

sudo -u hdfs hdfs dfsadmin -safemode enter
sudo -u hdfs hdfs dfsadmin -saveNamespace 
  1. Can some one let me know why there is a difference in the above steps?
  2. Is it just sufficient to enter in -safemode before doing the upgrade?
  3. If yes what does -rollingUpgrade started do then?
  4. In the cloudera documentation I am not seeing anything about -safemode leave. When it will leave the safemode? Will it auto leave the safemode ?