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Hadoop:Name node and data node replacement

+3 votes

I am trying to understand,how to recover a Name node or Data node failure in case if those nodes are unable to come up due to unexpected issues.

Is there a way to replace Name node with new name node without loosing data.I mean new Name node should have all the data from original Name node. Similarly for Data node.

posted Dec 9, 2013 by Satish Mishra

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1 Answer

+2 votes

To recover a NN, you probably want to use the HA feature. If not, try writing your edits to a nfs volume in additional to the local fs.

There is no need to recover a DN. The NN compensates for a lost DN by using the other remaining replicas to create a new replica on another DN.

answer Dec 9, 2013 by Majula Joshi
Thanks for your response.
You mean NN will always try to maintain number of replicas as configured even if one DN goes down and unable to come up?
Yes you are right. It will periodically checks the under replicated blocks information and place those blocks on available data nodes if required.
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+2 votes

Did any one got these error before, please help

ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: error processing WRITE_BLOCK operation  src: /xxxxxxxx:39000 dst: /xxxxxx:50010

at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.(
at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(
at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(
at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(
2015-01-11 04:13:21,846 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: IOException in offerService
WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Slow BlockReceiver write packet to mirror took 657ms (threshold=300ms)
+1 vote

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I want to spread I/O since I have ten disks per node, so should I set a comma-separated list of directories (which are on different disks) to "hadoop.tmp.dir" ?

+3 votes

As I studied that data distribution, load balancing, fault tolerance are implicit in Hadoop. But I need to customize it, can we do that?

0 votes

I've been trying to secure block data transferred by HDFS. I added below to hdfs-site.xml and core-site xml to the data node and name node and restart both.

When I try to put a file from the hdfs command line shell, the operation fails with "connection is reset" and I see following from the datanode log:

"org.apache.hadoop.hdfs.server.datanode.DataNode: Failed to read expected encryption handshake from client a / Perhaps the client is running an older version of Hadoop which does not support encryption"

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