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Date: Mon, 23 Jul 2012 10:55:33 +0000 (UTC)
From: "nkeywal (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
Message-ID: <1240240198.90526.1343040934478.JavaMail.jiratomcat@issues-vm>
Subject: [jira] [Created] (HDFS-3702) Add an option for NOT writing the
 blocks locally if there is a datanode on the same box as the client
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nkeywal created HDFS-3702:
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             Summary: Add an option for NOT writing the blocks locally if there is a datanode on the same box as the client
                 Key: HDFS-3702
                 URL: https://issues.apache.org/jira/browse/HDFS-3702
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: hdfs client
    Affects Versions: 2.0.0-alpha, 1.0.3
            Reporter: nkeywal
            Priority: Minor


This is useful for Write-Ahead-Logs: these files are writen for recovery only, and are not read when there are no failures.

Taking HBase as an example, these files will be read only if the process that wrote them (the 'HBase regionserver') dies. This will likely come from a hardware failure, hence the corresponding datanode will be dead as well. So we're writing 3 replicas, but in reality only 2 of them are really useful.


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