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From Cameron McKenzie <mckenzie....@gmail.com>
Subject Re: Q about majority voting, # of nodes, even node number
Date Thu, 16 Jan 2014 05:05:43 GMT
My understanding (which is admittedly limited):

There are 2 nodes left out of 3, so when both machines respond they will
get 2/3 of the vote, thus forming a majority. If you only had 2 machines in
your cluster for example, then if 1 died, then the others vote would only
make up 1/2 of the vote, which is not the majority, so you get no extra
redundancy in having 2 machines over having 1.


On Thu, Jan 16, 2014 at 3:59 PM, Otis Gospodnetic <
otis.gospodnetic@gmail.com> wrote:

> Hi,
>
> Somebody asked me recently and I "got stuck" trying to explain this.
> When people ask how many ZK nodes they should have a common answer is "odd
> number: 3 or 5 or ...", so ZK can do majority voting.  Correct so far?
> Another reason is for HA - if one ZK node dies, there are still 2 of them
> left.  And this is where I am missing something core - with just 2 nodes
> left, how can ZK do majority voting now?
>
> Thanks,
> Otis
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