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From James Seigel <ja...@tynt.com>
Subject Re: Two questions.
Date Thu, 04 Nov 2010 02:28:35 GMT
Option 1 = good

Sent from my mobile. Please excuse the typos.

On 2010-11-03, at 8:27 PM, "shangan" <shangan@corp.kaixin001.com> wrote:

> 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.
> 2010-11-04 
> shangan
> 发件人: Raj V 
> 发送时间: 2010-11-04  10:05:44 
> 收件人: common-user 
> 抄送: 
> 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 
> options.
> 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/
> Raj
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