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https://issues.apache.org/jira/browse/HADOOP-3034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12579695#action_12579695
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Konstantin Shvachko commented on HADOOP-3034:
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Sounds like decommission feature.
http://wiki.apache.org/hadoop/FAQ#17
> Need to be able to evacuate a datanode
> --------------------------------------
>
> Key: HADOOP-3034
> URL: https://issues.apache.org/jira/browse/HADOOP-3034
> Project: Hadoop Core
> Issue Type: Improvement
> Reporter: Ted Dunning
>
> It would be very helpful if there were some way to evacuate data from one or
> more nodes.
> This scenario arise fairly often when several nodes need to be powered down
> at nearly the same time. Currently, they can only be taken down a few at a
> time (n-1 nodes at a time where n is the replication factor) and then you
> have to wait until all files on these nodes have been replicated.
> One implementation would be to be to allow the nodes in question be put into
> read only mode and mark all blocks on those nodes as not counting as
> replicants. This should cause the namenode to copy these blocks and as soon
> as fsck shows no under-replicated files, the nodes will be known to be clear
> for power-down.
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