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https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242592#comment-13242592
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Sanjay Radia commented on HDFS-3077:
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*JournalDaemons or Bookies on Datanodes (Slave nodes) vs "Master" nodes*
* Slave nodes such as Datanodes are decommissioned for various reasons. This is
automatically handled and is
a simple process that makes the operations of Hadoop simple. Hence if we add a
Journal Daemon (or thread) or Bookie to the slave nodes it makes the system
harder to manage.
* It is preferable to run the Journal Daemons or Bookies on the master nodes -
NN, ZK, JT etc.
> 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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