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. > -- Connect to me at http://www.facebook.com/dhruba
