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From "M. C. Srivas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1539) prevent data loss when a cluster suffers a power loss
Date Wed, 22 Dec 2010 02:18:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12974017#action_12974017
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M. C. Srivas commented on HDFS-1539:
------------------------------------

Dhruba, so if there's a file with 20 blocks on 20 different servers, with 3 replicas each,
we might potentially end up sync'ing 41 servers (= 1 primary + 20*2 replicas) when closing
the file, correct?

> prevent data loss when a cluster suffers a power loss
> -----------------------------------------------------
>
>                 Key: HDFS-1539
>                 URL: https://issues.apache.org/jira/browse/HDFS-1539
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node, hdfs client, name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: syncOnClose1.txt
>
>
> we have seen an instance where a external outage caused many datanodes to reboot at around
the same time.  This resulted in many corrupted blocks. These were recently written blocks;
the current implementation of HDFS Datanodes do not sync the data of a block file when the
block is closed.
> 1. Have a cluster-wide config setting that causes the datanode to sync a block file when
a block is finalized.
> 2. Introduce a new parameter to the FileSystem.create() to trigger the new behaviour,
i.e. cause the datanode to sync a block-file when it is finalized.
> 3. Implement the FSDataOutputStream.hsync() to cause all data written to the specified
file to be written to stable storage.

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