What action occurs automatically on a cluster when a DataNode is marked as dead?

Question

Options

• AThe NameNode forces re-replication of all the blocks which were stored on the dead DataNode.
• BThe next time a client submits job that requires blocks from the dead DataNode, the JobTracker receives
• CThe replication factor of the files which had blocks stored on the dead DataNode is temporarily reduced,
• DThe NameNode informs the client which write the blocks that are no longer available; the client then

• A
  82% (37)
• B
  4% (2)
• C
  11% (5)
• D
  2% (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. Note: If the Name Node stops receiving heartbeats from a Data Node it presumes it to be dead and any data it had to be gone as well. Based on the block reports it had been receiving from the dead node, the Name Node knows which copies of blocks died along with the node and can make the decision to re-replicate those blocks to other Data Nodes. It will also consult the Rack Awareness data in order to maintain thetwo copies in one rack, one copy in another rackreplica rule when deciding which Data Node should receive a new copy of the blocks. NameNode Handles data node failures'

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