How does the NameNode know DataNodes are available on a cluster running MapReduce v1 (MRv1)

Question

Options

• ADataNodes listed in the dfs.hosts file. The NameNode uses as the definitive list of available DataNodes.
• BDataNodes heartbeat in the master on a regular basis.
• CThe NameNode broadcasts a heartbeat on the network on a regular basis, and DataNodes respond.
• DThe NameNode send a broadcast across the network when it first starts, and DataNodes respond.

• A
  16% (4)
• B
  72% (18)
• C
  8% (2)
• D
  4% (1)

Explanation

How NameNode Handles data node failures? NameNode periodically receives a Heartbeat and a Blockreport from each of the DataNodes in the cluster. Receipt of a Heartbeat implies that the DataNode is functioning properly. A Blockreport contains a list of all blocks on a DataNode. When NameNode notices that it has not recieved a hearbeat message from a data node after a certain amount of time, the data node is marked as dead. Since blocks will be under replicated the system begins replicating the blocks that were stored on the dead datanode. The NameNode Orchestrates the replication of data blocks from one datanode to another. The replication data transfer happens directly between datanodes and the data never passes through the namenode. NameNode Handles data node failures?

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