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From "Ted Dunning (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-3034) Need to be able to evacuate a datanode
Date Tue, 18 Mar 2008 00:46:25 GMT
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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