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https://issues.apache.org/jira/browse/HDFS-957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854131#action_12854131
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Todd Lipcon commented on HDFS-957:
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I think this is still a good idea, even with that bug fixed. The extra
safeguard doesn't really cost us anything, and the fsync() is important when
using a FS with delayed allocation.
> FSImage layout version should be only once file is complete
> -----------------------------------------------------------
>
> Key: HDFS-957
> URL: https://issues.apache.org/jira/browse/HDFS-957
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hdfs-957.txt
>
>
> Right now, the FSImage save code writes the LAYOUT_VERSION at the head of the
> file, along with some other headers, and then dumps the directory into the
> file. Instead, it should write a special IMAGE_IN_PROGRESS entry for the
> layout version, dump all of the data, then seek back to the head of the file
> to write the proper LAYOUT_VERSION. This would make it very easy to detect
> the case where the FSImage save got interrupted.
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