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From George Kousiouris <gkous...@mail.ntua.gr>
Subject Re: Hang when add/remove a datanode into/from a 2 datanode cluster
Date Fri, 21 Jun 2013 09:34:28 GMT

Hi,

I think i have faced this before, the problem is that you have the rep 
factor=3 so it seems to hang because it needs 3 nodes to achieve the 
factor (replicas are not created on the same node). If you set the 
replication factor=2 i think you will not have this issue. So in general 
you must make sure that the rep factor is <= to the available datanodes.

BR,
George

On 6/21/2013 12:29 PM, sam liu wrote:
> Hi,
>
> I encountered an issue which hangs the decommission operatoin. Its steps:
> 1. Install a Hadoop 1.1.1 cluster, with 2 datanodes: dn1 and dn2. And, 
> in hdfs-site.xml, set the 'dfs.replication' to 2
> 2. Add node dn3 into the cluster as a new datanode, and did not change 
> the 'dfs.replication' value in hdfs-site.xml and keep it as 2
> note: step 2 passed
> 3. Decommission dn3 from the cluster
>
> Expected result: dn3 could be decommissioned successfully
>
> Actual result: decommission progress hangs and the status always be 
> 'Waiting DataNode status: Decommissioned'
>
> However, if the initial cluster includes >= 3 datanodes, this issue 
> won't be encountered when add/remove another datanode.
>
> Also, after step 2, I noticed that some block's expected replicas is 
> 3, but the 'dfs.replication' value in hdfs-site.xml is always 2!
>
> Could anyone pls help provide some triages?
>
> Thanks in advance!


-- 
---------------------------

George Kousiouris, PhD
Electrical and Computer Engineer
Division of Communications,
Electronics and Information Engineering
School of Electrical and Computer Engineering
Tel: +30 210 772 2546
Mobile: +30 6939354121
Fax: +30 210 772 2569
Email: gkousiou@mail.ntua.gr
Site: http://users.ntua.gr/gkousiou/

National Technical University of Athens
9 Heroon Polytechniou str., 157 73 Zografou, Athens, Greece


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