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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13399804#comment-13399804
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Brandon Li commented on HDFS-3077:
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{quote}So, the recovery process should complete in far less than 1 second given 
the transfer time for such a segment would be <~50ms. Hence the chances of a 
crash during this timeframe are vanishingly small.{quote}
JN can be inaccessible to another JN for many reasons, such as network 
partition. But, I agree a list of URL in step2 is good enough for now.
                
> Quorum-based protocol for reading and writing edit logs
> -------------------------------------------------------
>
>                 Key: HDFS-3077
>                 URL: https://issues.apache.org/jira/browse/HDFS-3077
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: ha, name-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-3077-partial.txt, qjournal-design.pdf, 
> qjournal-design.pdf
>
>
> Currently, one of the weak points of the HA design is that it relies on 
> shared storage such as an NFS filer for the shared edit log. One alternative 
> that has been proposed is to depend on BookKeeper, a ZooKeeper subproject 
> which provides a highly available replicated edit log on commodity hardware. 
> This JIRA is to implement another alternative, based on a quorum commit 
> protocol, integrated more tightly in HDFS and with the requirements driven 
> only by HDFS's needs rather than more generic use cases. More details to 
> follow.

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