How should configuration files of Active and Backup NameNode should differ from 
each other?

Assume that our Active NameNode died, do we need to anything further DNS record 
change? We start our Backup NameNode with "-backup" argument.  How to convert 
role to active?



From: Dhruba Borthakur 
Sent: Friday, October 08, 2010 12:49 AM
To: hdfs-user@hadoop.apache.org 
Subject: Re: Backup NameNode


ActiveNameNode and BackupNamenode do not automatically  exchange roles ever.  
DataNodes are not informed. One can use Virtual IP failover  or DNS to switch 
so that DataNodes need not know that the Namenode has moved from one machine to 
another. 


hope this helps,
dhruba


On Wed, Oct 6, 2010 at 10:07 PM, Ozcan ILIKHAN <ilik...@cs.wisc.edu> wrote:

  Hi all,

  Following questions are specific to v0.21.0.

  From the user guide it is not clear enough how Active NameNode and Backup 
Namenode take over role from each other, how DateNode are informed if active 
NameNode  fails (or do they need to be informed?). What is happening in 
disaster scnerios.

  While configuring cluster, assume 1 active NameNode, 1 Backup NameNode, 1 
Chekpoint NameNode, and the rest of the cluster is assumed to be DataNodes.  
Which parameters for these 4 types of nodes' hdfs-site.xml and core-site.xml  
should set, and how should they (config files of 4 type of nodes ) differ from 
each other.

  By the way, in order to understand certain functionalities, most of the time 
we need to go deep into source code. I think it will be good to enrich Hadoop 
(especially HDFS) documentation.

  Thanks in advance,
  Ozcan.



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