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From "Zhu Huijun" <nautilu...@gmail.com>
Subject Specifying the positions of replicas
Date Mon, 25 Feb 2008 22:31:31 GMT
Hi, all,

Currently our group want to try some new data layout schemes on Hadoop, but
I encounter some problems.

In Hadoop, each block has 3 replicas by default. It is said in the documents
that two of them are put randomly in the same rack, and the third is put at
another rack. This procedure is also clear in the source code of the class
org.apache.hadoop.dfs.ReplicationTargetChooser.

What I did was adding a simple System.out.println("function name") clause in
each function in ReplicationTargetChooser, and intended to check which ones
are called to select the target nodes for replicas. However, when I use
"./bin/hadoop dfs -copyFromLocal" command to copy some files from the local
file system to HDFS, it seems none of the functions in the
ReplicationTargetChooser is called, because nothing is printed out on the
screen or the log files.

I preciate if someone can tell me where I can modify to control the target
nodes of replicas. Thank you!

Have a nice day!

Huijun Zhu

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