Here, you should also mention the function of the Secondary NameNode while answering the later part of this question so as to provide clarity:
A Secondary NameNode is a helper daemon that performs checkpointing in HDFS. No, it is not a backup or a substitute node for the NameNode. It periodically, takes the edit logs (meta data file) from NameNode and merges it with the FsImage (File system Image) to produce an updated FsImage as well as to prevent the Edit Logs from becoming too large.
