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  1. Documentation
  2. DOCS-2008

Geographically distributed replica set - why majority of voting nodes in one place?

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      In http://docs.mongodb.org/manual/tutorial/deploy-geographically-distributed-replica-set/, the documentation claims that you should "Ensure that a majority of the voting members are within a primary facility", however:

      1) The documentation offers no explanation for why you should ensure the majority of voting members are all in one place. This seems counter-intuitive, as if this entire data center goes down, it will take a majority of the voting nodes with it, rendering the replica set unable to elect a new master. It seems that placing two nodes an the arbiter each in three different locations would be a better solution.

      2) The latest version of this documentation in master states: "For more information on the need to keep the voting majority on one site, see
      :doc:`/core/replica-set-elections`". The referenced page, however, only talks about network partitions, and not about the failure of a data center.

      https://github.com/mongodb/docs/blob/master/source/tutorial/deploy-geographically-distributed-replica-set.txt#L39

      3) At the bottom of the document is this diagram:

      http://docs.mongodb.org/manual/_images/replica-set-three-data-centers.png

      Where there are clearly not a majority of voting nodes in a single data center.

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            kay.kim@mongodb.com Kay Kim (Inactive)
            jwalton Jason Walton
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              Created:
              Updated:
              Resolved:
              10 years, 20 weeks, 5 days ago