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From Tim Bain <tb...@alumni.duke.edu>
Subject Re: clustering architecture
Date Tue, 03 May 2016 04:46:02 GMT
It's not possible to have a quorum (i.e. > 50%) in all scenarios when you
only have two groupings and both of them could disappear entirely.  By
definition, to have a quorum after the loss of one grouping, the lost
grouping must be < 50% and the one that remains must be > 50%, so in the
inverse situation you can't possibly have a quorum.  This is why three is
typically the number used to ensure survivability of the loss of a single
item (whether an "item" is a process, a host, a rack, or a datacenter).  So
either you need a third datacenter in a third location, or you need to put
two groupings in a single geographic site (in separate buildings, for
example, or different floors or rooms, or on the other side of town), and
accept that you're sacrificing the ability to survive certain catastrophes
in order to save the cost of locating the third datacenter somewhere
geographically distant.

Tim

On Sun, May 1, 2016 at 8:37 AM, sekaijin <jean-yves.terrien@sap.aphp.fr>
wrote:

> Hi
>
> There is a little thing I do not understand in the election of the master.
>
> I have two geographic site (Paris, Versailles).
> the quorum is (n / 2) +1
> if I have two servers in each site
> the quorum is (4/2) +1 = 3
> so if I have a blackout on the site (eg fire) I do not have the quorum
> because I have only two servers
>
> if I have two server on a site and on the other
> the quorum is (3/2) +1 = 2
> so if I have a blackout on first site (eg fire) I do not have a quorum
> because I have only one server
>
> It is impossible to secure the cluster?
>
> A+JYT
>
>
>
> --
> View this message in context:
> http://activemq.2283324.n4.nabble.com/clustering-architecture-tp4711412p4711418.html
> Sent from the ActiveMQ - User mailing list archive at Nabble.com.
>

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