HDFS error: could only be replicated to 0 nodes, instead of 1

WARNING: The following will destroy ALL data on HDFS. Do not execute the steps in this answer unless you do not care about destroying existing data!!

You should do this:

1. stop all hadoop services
2. delete dfs/name and dfs/data directories
3. hdfs namenode -format Answer with a capital Y
4. start hadoop services

Also, check the diskspace in your system and make sure the logs are not warning you about it.

This is your issue - the client can't communicate with the Datanode. Because the IP that the client received for the Datanode is an internal IP and not the public IP. Take a look at this

http://www.hadoopinrealworld.com/could-only-be-replicated-to-0-nodes/

Look at the sourcecode from DFSClient$DFSOutputStrem (Hadoop 1.2.1)

//// Connect to first DataNode in the list.//success = createBlockOutputStream(nodes, clientName, false);if (!success) {  LOG.info("Abandoning " + block);  namenode.abandonBlock(block, src, clientName);  if (errorIndex < nodes.length) {    LOG.info("Excluding datanode " + nodes[errorIndex]);    excludedNodes.add(nodes[errorIndex]);  }  // Connection failed. Let's wait a little bit and retry  retry = true;}

The key to understand here is that Namenode only provide the list of Datanodes to store the blocks. Namenode does not write the data to the Datanodes. It is the job of the Client to write the data to the Datanodes using the DFSOutputStream . Before any write can begin the above code make sure that the Client can communicate with the Datanode(s) and if the communication fails to the Datanode, the Datanode is added to the excludedNodes .

Look at following:

By seeing this exception(could only be replicated to 0 nodes, instead of 1), datanode is not available to Name Node..

This are the following cases Data Node may not available to Name Node

1. Data Node disk is Full

2. Data Node is Busy with block report and block scanning

3. If Block Size is Negative value(dfs.block.size in hdfs-site.xml)

4. while write in progress primary datanode goes down(Any n/w fluctations b/w Name Node and Data Node Machines)

5. when Ever we append any partial chunk and call sync for subsequent partial chunk appends client should store the previous data in buffer.

For example after appending "a" I have called sync and when I am trying the to append the buffer should have "ab"

And Server side when the chunk is not multiple of 512 then it will try to do Crc comparison for the data present in block file as well as crc present in metafile. But while constructing crc for the data present in block it is always comparing till the initial Offeset Or For more analysis Please the data node logs

Reference: http://www.mail-archive.com/hdfs-user@hadoop.apache.org/msg01374.html