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Explain the difference between NameNode, Backup Node and Checkpoint NameNode?

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Explain the difference between NameNode, Backup Node and Checkpoint NameNode?
posted Dec 22, 2016 by Karthick.c

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A few days ago, I modified dfs.datanode.data.dir of a datanode () to reduce disks. so two disks were excluded from dfs.datanode.data.dir, after the datanode was restarted, I expected that the namenode would update block locations. In other words, I thought the namenode should remove from block locations associated with blocks which were stored on excluded disks, but the namenode didnt update the block locations...

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