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HDFS >> mail # user >> Re: Hang when add/remove a datanode into/from a 2 datanode cluster

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Re: Hang when add/remove a datanode into/from a 2 datanode cluster


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.


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
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