Which happens if the NameNode crashes?
HDFS becomes unavailable until the NameNode is restored.
The Secondary NameNode seamlessly takes over and there is no service interruption.
HDFS becomes unavailable to new MapReduce jobs, but running jobs will continue until
HDFS becomes temporarily unavailable until an administrator starts redirecting client requests
to the Secondary NameNode.
The NameNode is a Single Point of Failure for the HDFS Cluster. When the
NameNode goes down, the file system goes offline.
Reference:24 Interview Questions & Answers for Hadoop MapReduce developers,What is a
NameNode? How many instances of NameNode run on a Hadoop Cluster?