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What happens if data node restarts by itself ? any effect to the data present in that node?

 
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Re: What happens if data node restarts by itself ? any effect to the data present in that node?

Assuming you have multiple data nodes and a replication factor greater than 1, you should not experience any outage if a single DN restarts.  Redundancy and data availability are built into the HDFS Architecture.  The caveat to this is that really small test clusters, like 2 or 3 datanodes, or if you have HDFS block replication set to 1 or 2, you could be subject to data loss if a single DN goes down.  If you correctly architect your cluster, a single DN dropping or restarting is just another day in normal operation for HDFS.

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