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https://issues.apache.org/jira/browse/HADOOP-3034?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nigel Daley reopened HADOOP-3034:
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> 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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