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From Narasingu Ramesh <ramesh.narasi...@gmail.com>
Subject Re: what happens when a datanode rejoins?
Date Tue, 11 Sep 2012 09:08:28 GMT
Hi Mehul,
             DataNode rejoins take care of only NameNode.
Thanks & Regards,
Ramesh.Narasingu

On Tue, Sep 11, 2012 at 2:36 PM, Mehul Choube <Mehul_Choube@symantec.com>wrote:

> > 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.****
>
> What happens when the datanode rejoins after namenode has already
> re-replicated the blocs it was managing?****
>
> Will namenode ask the datanode to discard the blocks and start managing
> new blocks?****
>
> Or will namenode discard the new blocks which were replicated due to
> unavailability of this datanode?****
>
> ** **
>
> ** **
>
> ** **
>
> Thanks,****
>
> Mehul****
>
> ** **
>
> ** **
>
> *From:* George Datskos [mailto:george.datskos@jp.fujitsu.com]
> *Sent:* Tuesday, September 11, 2012 12:56 PM
> *To:* user@hadoop.apache.org
> *Subject:* Re: what happens when a datanode rejoins?****
>
> ** **
>
> 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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