Your Hadoop cluster contains nodes in three racks. Choose which scenario results if you leave the
dfs.hosts property in the NameNode’s configuration file empty (blank)?
A.
The NameNode will update dfs.hosts property to include machines running the DataNode
daemon on the next NameNode reboot or with a dfsadmin –refreshNodes.
B.
Any machine running the DataNode daemon can immediately join the cluster.
C.
Presented with a blank dfs.hosts property, the NameNode will permit DataNodes specified in
mapred.hosts to join the cluster.
D.
No new can be added to the cluster until you specify them in the dfs.hosts file.
Explanation:
The dfs.hosts and mapred.hosts properties allow an administrator to supply a file
containing an approved list of hostnames. If a machine is not in this list, it will be denied access to
the cluster. This can be used to enforce policies regarding which teams of developers have access
to which MapReduce sub-clusters. These are configured in exactly the same way as the excludes
file.
Reference:
Apache Hadoop , Module 7: Managing a Hadoop Cluster
Not Agree with answer
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Correct answer is D
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Not agree.. because we have kept dfs.host property in config file empty and not actual dfs.host file. If the dfs.host property is empty then “Any machine running the DataNode daemon can immediately join the cluster.”
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