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https://issues.apache.org/jira/browse/HDFS-1539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12973125#action_12973125
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Todd Lipcon commented on HDFS-1539:
-----------------------------------

Yep, I certainly didn't intend to block this JIRA. What you've done here is 
definitely prudent, and we can debate/benchmark turning it on by default in 
another JIRA.

> 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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