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From "Ruyue Ma (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-630) In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when locating the next block.
Date Fri, 18 Sep 2009 07:06:57 GMT
In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when
locating the next block.
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                 Key: HDFS-630
                 URL: https://issues.apache.org/jira/browse/HDFS-630
             Project: Hadoop HDFS
          Issue Type: New Feature
          Components: hdfs client
    Affects Versions: 0.20.1, 0.21.0
            Reporter: Ruyue Ma
            Assignee: Ruyue Ma
            Priority: Minor
             Fix For: 0.21.0


created from hdfs-200.

If during a write, the dfsclient sees that a block replica location for a newly allocated
block is not-connectable, it re-requests the NN to get a fresh set of replica locations of
the block. It tries this dfs.client.block.write.retries times (default 3), sleeping 6 seconds
between each retry ( see DFSClient.nextBlockOutputStream).

This setting works well when you have a reasonable size cluster; if u have few datanodes in
the cluster, every retry maybe pick the dead-datanode and the above logic bails out.

Our solution: when getting block location from namenode, we give nn the excluded datanodes.
The list of dead datanodes is only for one block allocation.

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