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From sam liu <samliuhad...@gmail.com>
Subject Hang when add/remove a datanode into/from a 2 datanode cluster
Date Fri, 21 Jun 2013 09:29:33 GMT

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!

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