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https://issues.apache.org/jira/browse/HDFS-1539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12974258#action_12974258
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dhruba borthakur commented on HDFS-1539:
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if there is a file with 20 blocks and each block has three replicas each, then
there will be a total of 60 fflush calls, this does not matter on the number of
servers.
> 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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