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Placing Namenode in safemode and Perform checkpoint

Normally in real environment secondary node performs checkpoint operation and keep syncing with active namenode to keep latest FSimage.  In HA environment active namenode writes edit log into  journal node and standby node go and get the edit log and create new FSimage.

[hdfs@datanode1 ~]$ hdfs dfsadmin -safemode get
Safe mode is OFF

[hdfs@datanode1 ~]$ hdfs dfsadmin -safemode enter
Safe mode is ON

[hdfs@datanode1 ~]$ hdfs dfsadmin -saveNamespace       (checkpoint command)
Save namespace successful

[hdfs@datanode1 ~]$ hdfs dfsadmin -safemode leave
Safe mode is OFF



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