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From Panshul Whisper <ouchwhis...@gmail.com>
Subject Re: hadoop namenode recovery
Date Tue, 15 Jan 2013 03:31:25 GMT
Hello Bejoy,

Thank you for the information.
about the Hadoop HA 2.x releases, they are in Alpha phase and I cannot use
them for production. For my requirements, the cluster is supposed to be
extremely Available. Availability is of highest concern. I have looked into
different distributions as well.. such as Hortonworks, they also have the
same problem of Single point of failure. And are waiting for Apache to
release the Hadoop 2.x.

I was wondering, if I can somehow configure two Name Nodes on the same
Network with the same IP Address, but the second name node is redirected
only after the failure of the primary, that might help in automatic
resolution of this problem. all the slaves are connecting to the Name Node
with a network alias in their /etc/hosts file.
I am trying to implement something like this in the cluster:

please suggest if this is possible.

Thanks for your time.

On Mon, Jan 14, 2013 at 7:11 PM, <bejoy.hadoop@gmail.com> wrote:

> **
> Hi Panshul
> SecondaryNameNode is rather known as check point node. At periodic
> intervals it merges the editlog from NN with FS image to prevent the edit
> log from growing too large. This is its main functionality.
> At any point the SNN would have the latest fs image but not the updated
> edit log. If NN goes down and if you don't have an updated copy of edit log
> you can use the fsImage from SNN for restoring. In that case you lose the
> transactions in edit log.
> SNN is not a backup NN it is just a check point node.
> Two or more NN are not possible in 1.x releases but federation makes it
> possible with 2.x releases. Federation is for different purpose, you should
> be looking at hadoop HA currently with 2.x releases.
> Regards
> Bejoy KS
> Sent from remote device, Please excuse typos
> ------------------------------
> *From: * Panshul Whisper <ouchwhisper@gmail.com>
> *Date: *Mon, 14 Jan 2013 19:04:24 -0800
> *To: *<user@hadoop.apache.org>; <bejoy.hadoop@gmail.com>
> *Subject: *Re: hadoop namenode recovery
> thank you for the reply.
> Is there a way with which I can configure my cluster to switch to the
> Secondary Name Node automatically in case of the Primary Name Node failure?
> When I run my current Hadoop, I see the primary and secondary both Name
> nodes running. I was wondering what is that Secondary Name Node for? and
> where is it configured?
> I was also wondering, is it possible to have two or more Name nodes
> running in the same cluster?
> Thanks,
> Regards,
> Panshul.
> On Mon, Jan 14, 2013 at 6:50 PM, <bejoy.hadoop@gmail.com> wrote:
>> **
>> Hi Panshul,
>> Usually for reliability there will be multiple dfs.name.dir configured.
>> Of which one would be a remote location such as a nfs mount.
>> So that even if the NN machine crashes on a whole you still have the fs
>> image and edit log in nfs mount. This can be utilized for reconstructing
>> the NN back again.
>> Regards
>> Bejoy KS
>> Sent from remote device, Please excuse typos
>> ------------------------------
>> *From: * Panshul Whisper <ouchwhisper@gmail.com>
>> *Date: *Mon, 14 Jan 2013 17:25:08 -0800
>> *To: *<user@hadoop.apache.org>
>> *ReplyTo: * user@hadoop.apache.org
>> *Subject: *hadoop namenode recovery
>> Hello,
>> Is there a standard way to prevent the failure of Namenode crash in a
>> Hadoop cluster?
>> or what is the standard or best practice for overcoming the Single point
>> failure problem of Hadoop.
>> I am not ready to take chances on a production server with Hadoop 2.0
>> Alpha release, which claims to have solved the problem. Are there any other
>> things I can do to either prevent the failure or recover from the failure
>> in a very short time.
>> Thanking You,
>> --
>> Regards,
>> Ouch Whisper
>> 010101010101
> --
> Regards,
> Ouch Whisper
> 010101010101

Ouch Whisper

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