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From Alberto Chiusole <alberto.chiusol...@gmail.com>
Subject Small mistake (?) in doc about HA with Journal Nodes
Date Mon, 05 Dec 2016 19:32:46 GMT
Hi all,
I'm Alberto Chiusole, an Italian computer science student and 
open-source fan.
I'm currently performing a small research to expose to my fellow 
students the Hadoop project, and this is my first post in this ML.

I think I spotted I small mistake in the HDFS documentation regarding 
achieving HA with the Quorum Journal Manager [1], section "Hardware 
resources", paragraph "JournalNode machines": it's stated:
"""
The JournalNode daemon is relatively lightweight, so these daemons may 
reasonably be collocated on machines with other Hadoop daemons, for 
example NameNodes, the JobTracker, (...)
"""

Is "NameNodes" a typo and you meant "DataNode" instead? Aren't the 
JournalNodes meant to survive in case of a failure of the NameNodes? Why 
should I place a JournalNode on the same machine that contains the log I 
need to synchronize?


Moreover I have a quick question on the same topic: why do you suggest 
to place an odd numbers of machines as JournalNodes in order to increase 
the Fault Tolerance?


Regards,
Alberto Chiusole


[1]: 
https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithQJM.html#Hardware_resources



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