Re: When to use Arbiter volumes and quorum options?

Ravishankar N <ravishankar@xxxxxxxxxx> · Sat, 26 Nov 2016 18:37:09 +0530



    On 11/26/2016 04:54 PM, Alexandr
      Porunov wrote:

    
        Hello,
        

        I am using GlusterFS 3.8.5. I wonder to know when to use
          Arbiter volumes and quorum options in GlusterFS and what
          difference between them?
        

        I tried to achive a split-brain in a replicated voulume 3
          but couldn't. Does GlusterFS manage split-brain situations
          automaticaly?
        

        I tried following:
        node1, node2, node3 is the nodes with a replicated volume.
        I have created a network crash between node1 and node3 but
          node1 and node3 still can speak with node2. When I write a
          file to node1 it automatically creates on node2 and node3.
          When I write a file to node3 it automaticaly creates on node2
          and node1.
        

        I tried to crash node1 then write to node3 and then crash a
          node3 and recover node1. Still it works just fine. I tried to
          crash two nodes and then write to the healthy node and it
          doesn't work. After I have run one more node it started work.
        

        Is it possible to achive a split-brain in a GlusterFS
          cluster 3.8.5? If yes then how and what options we have to set
          to prevent split-brain? If no then why do we need an arbiter
          and quorum options?
        

    Split-brains are possible in replica-2 volumes. They don't occur in
    replica-3 volumes or arbiter-volumes. Client-quorum is enabled and
    set to 'auto' when you create replica-3 or arbiter vols. You're not
    supposed to change it. Arbiter vols can be used if you want to avoid
    split-brains but don't want to invest in a 3rd data brick for
    replica-3. Of course, the availability of arbiter is less compared
    to replica-3 because we don't store the actual file content in the
    3rd (arbiter) brick.

    
    You can find more information @
http://gluster.readthedocs.io/en/latest/Administrator%20Guide/arbiter-volumes-and-quorum/
    and
http://events.linuxfoundation.org/sites/events/files/slides/glusterfs-arbiter-VAULT-2016.pdf

    
    Regards,

    Ravi

    
        Sincerely,
        Alexandr
      
      
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