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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5713) File write fails after data node goes down
Date Sun, 10 May 2009 10:33:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5713?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12707773#action_12707773
] 

dhruba borthakur commented on HADOOP-5713:
------------------------------------------

Your approach looks good but the client does not conclusively know whether the datanode is
really dead, transient error or network failure. Also, we have not seen this problem occuring
in a a resonable size cluster (i.e. #datanodes > 5 or so). Do you feel that the problem
you mentioned occurs in a reasonable size cluster and warrants the additional complexity in
the client?

Maybe you can set dfs.client.block.write.retries in your configuration to a large value to
alleviate this problem?



> File write fails after data node goes down
> ------------------------------------------
>
>                 Key: HADOOP-5713
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5713
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Alban Chevignard
>         Attachments: failed_write.patch
>
>
> If a data node goes down while a file is being written do HDFS, the write fails with
the following errors:
> {noformat} 
> 09/04/20 17:15:39 INFO dfs.DFSClient: Exception in createBlockOutputStream java.io.IOException:
> Bad connect ack with firstBadLink 192.168.0.66:50010
> 09/04/20 17:15:39 INFO dfs.DFSClient: Abandoning block blk_-6792221430152215651_1003
> 09/04/20 17:15:45 INFO dfs.DFSClient: Exception in createBlockOutputStream java.io.IOException:
> Bad connect ack with firstBadLink 192.168.0.66:50010
> 09/04/20 17:15:45 INFO dfs.DFSClient: Abandoning block blk_-1056044503329698571_1003
> 09/04/20 17:15:51 INFO dfs.DFSClient: Exception in createBlockOutputStream java.io.IOException:
> Bad connect ack with firstBadLink 192.168.0.66:50010
> 09/04/20 17:15:51 INFO dfs.DFSClient: Abandoning block blk_-1144491637577072681_1003
> 09/04/20 17:15:57 INFO dfs.DFSClient: Exception in createBlockOutputStream java.io.IOException:
> Bad connect ack with firstBadLink 192.168.0.66:50010
> 09/04/20 17:15:57 INFO dfs.DFSClient: Abandoning block blk_6574618270268421892_1003
> 09/04/20 17:16:03 WARN dfs.DFSClient: DataStreamer Exception: java.io.IOException:
> Unable to create new block.
> 	at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2387)
> 	at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.access$1800(DFSClient.java:1746)
> 	at org.apache.hadoop.dfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:1924)
> 09/04/20 17:16:03 WARN dfs.DFSClient: Error Recovery for block blk_6574618270268421892_1003
bad datanode[1]
> {noformat} 
> The tests were done with the following configuration:
> * Hadoop version 0.18.3
> * 3 data nodes with replication count of 2
> * 1 GB file write
> * 1 data node taken down during write
> This issue seems to be caused by the fact that there is a delay between the time a data
node goes down and the time it is marked as dead by the name node. This delay is unavoidable,
but the name node should not keep allocating new blocks to data nodes that are known to be
down by the client. Even by adjusting {{heartbeat.recheck.interval}}, there is still a window
during which this issue can occur.
> One possible fix would be to allow clients to exclude known bad data nodes when allocating
new blocks. See {{failed_write.patch}} for an example.

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