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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13229661#comment-13229661
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Todd Lipcon commented on HDFS-3077:
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>>We have a single writer, except for when we don't. During a failover, without
>>a STONITH capability,
>Without some sort of fencing, you're going to have to run agreement on every
>update. If this is acceptable, you could have just made the namenode a thin
>RPC layer on top of zookeeper, and you get fault tolerance for free.
Yea, as described in my comment this morning, there is a fencing operation
built into the logger daemons. Same as BK. So you only need a consensus about
recovery. It's the same thing as BK, similar to multi-paxos, etc -- the steady
state is fast and you pay costs at leader switchover.
> 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
>
> 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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