What is a Secondary Namenode? Is it a substitute to the Namenode?

1.	What is a Secondary Namenode? Is it a substitute to the Namenode?
Answer» The secondary Namenode constantly reads the data from the RAM of the Namenode and writes it into the hard disk or the file system. It is not a substitute to the Namenode, so if the Namenode fails, the entire Hadoop system goes down.

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