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From "shangan" <shan...@corp.kaixin001.com>
Subject Re: Two questions.
Date Thu, 04 Nov 2010 02:27:12 GMT
I don't think the first two options can work, even you stop the tasktracker these to-be-retired
nodes are still connected to the namenode.
Option 3 can work.  You only need to add this exclude file on the namenode, and it is an regular
file. Add a key named dfs.hosts.exclude to your conf/hadoop-site.xml file,The value associated
with this key provides the full path to a file on the NameNode's local file system which contains
a list of machines which are not permitted to connect to HDFS.

Then you can run the command bin/hadoop dfsadmin -refreshNodes, then the cluster will decommission
the nodes in the exclude file.This might take a period of time as the cluster need to move
data from those retired nodes to left nodes.

After this you can use these retired nodes as a new cluster.But remember to remove those nodes
from the slave nodes file and you can delete the exclude file afterward.



发件人: Raj V 
发送时间: 2010-11-04  10:05:44 
收件人: common-user 
主题: Two questions. 
1. I have a 512 node cluster. I need to have 32 nodes do something else. They 
can be datanodes but I cannot run any map or reduce jobs on them. So I see three 
1. Stop the tasktracker on those nodes. leave the datanode running.
2. Set  mapred.tasktracker.reduce.tasks.maximum and 
mapred.tasktracker.map.tasks.maximum to 0 on these nodes and make these final.
3. Use the parameter mapred.hosts.exclude. 
I am assuming that any of the three methods would work.  To start with, I went 
with option 3. I used a local file /home/hadoop/myjob.exclude and the file 
myjob.exclude had the hostname of one host per line ( hadoop-480 .. hadoop-511. 
But I see both map and reduce jobs being scheduled to all the 511 nodes. 
I understand there is an inherent inefficieny by running only the data node on 
these 32 nodess.
Here are my questions.
1. Will all three methods work?
2. If I choose method 3, does this file exist as a dfs file or a regular file. 
If regular file , does it need to exist on all the nodes or only the node where 
teh job is submitted?
Many thanks in advance/
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