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Subject: RE: What should be the majority in an ensemble for Zookeeper
Date: Fri, 4 Apr 2014 18:15:33 +0100
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I think there is quite a bit of confusion here. You don't select a majority,
the system does it for you. The only thing you need to select is the total
number of servers, and the text you're quoting is just trying to convince
you to use an odd number instead of an even number of servers.

Use 3 servers (total) if you want to tolerate one faulty server, 5 if you
want to tolerate 2 faulty servers, 7 if you want to tolerate 3 and so on.

Hope it is a bit better now.

-Flavio

> -----Original Message-----
> From: chaitanya_r [mailto:chaitanya_spring@yahoo.com]
> Sent: 03 April 2014 19:45
> To: zookeeper-user@hadoop.apache.org
> Subject: What should be the majority in an ensemble for Zookeeper
> 
> I am trying to understand Zookeeper using this book -  Zookeeper By Flavio
> Junqueira, Benjamin Reed
> <http://shop.oreilly.com/product/0636920028901.do>
> , it is mentioned that we need to select a majority of servers for quorum
as
> stated here:
> 
> "Say that we use four servers for an ensemble. A majority of servers is
> comprised of three servers. However, this system will only tolerate a
single
> crash, because a double crash makes the system lose majority.
> Consequently, with four servers, we can only tolerate a single crash, but
> quorums now are larger, which implies that we need more
> acknowledgments for each request.
> The bottom line is that we should always shoot for an odd number of
> servers."
> 
> Please help me in understanding this.
> 
> How do we select the majority of servers for a given ensemble?
> 
> Why does this statement say quorums now are larger and why do we need
> more acknowledgments for each request?
> 
> 
> 
> --
> View this message in context: http://zookeeper-
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> for-Zookeeper-tp7579721.html
> Sent from the zookeeper-user mailing list archive at Nabble.com.