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From Olivier Renault <orena...@hortonworks.com>
Subject Re: Journal Nodes in a multi-site environment
Date Wed, 11 Dec 2013 21:30:31 GMT
To get a quorum you need to have : number of QJM / 2 +1 so in case of 3 you
need 2 servers to be up. If you've got 3 QJM on each side, in case of
losing a DC, you will never get quorum as it will require 4 nodes. When you
lose your DC with the 2 QJMs, you could manually start Hadoop on the second
DC.

As a side note, Hadoop is not yet recommended as a multi DC solution.

Hope it helps.
Olivier


On 11 December 2013 21:49, Jeff Sposetti <jeff@hortonworks.com> wrote:

> Adding in some Hadoop folks to chime in here.
>
>
>
> On Wed, Dec 11, 2013 at 5:35 AM, Chadwick Banning <
> chadwickbanning@gmail.com> wrote:
>
>> Hi all,
>>
>> I have an Ambari 1.4/HDP 2.0.6 environment that is split between two data
>> centers -- a main site and a recovery site.  We have NameNode HA enabled
>> with automatic failover and the problem we are facing is how to divide the
>> journal nodes across both sites so that failover happens appropriately.
>>
>> It seems that only one site will always have a majority of journal nodes
>> and if that site NN were to go down, the other site NN would no longer be
>> able to start as it couldn't reach a majority of the journal nodes.
>>
>> Is there any way around this?  I know an odd number of journal nodes is
>> recommended but what would happen if we were to place an even number of
>> journal nodes at each site?
>>
>> Thanks for any input!
>>
>
>
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