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From George Datskos <george.dats...@jp.fujitsu.com>
Subject Re: what happens when a datanode rejoins?
Date Tue, 11 Sep 2012 07:25:38 GMT
Hi Mehul

> Some of the blocks it was managing are deleted/modified?
>

The namenode will asynchronously replicate the blocks to other datanodes 
in order to maintain the replication factor after a datanode has not 
been in contact for 10 minutes.

> The size of the blocks are now modified say from 64MB to 128MB?
>

Block size is a per-file setting so new files will be 128MB, but the old 
ones will remain at 64MB.

> What if the block replication factor was one (yea not in most 
> deployments but say incase) so does the namenode recreate a file once 
> the datanode rejoins?
>

(assuming you didn't perform a decommission) Blocks that lived only on 
that datanode will be declared "missing" and the files associated with 
those blocks will be not be able to be fully read, until the datanode 
rejoins.



George

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