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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 


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