[ovirt-users] why replica 3

[Richard Neuboeck]

On 04.09.15 10:02, Simone Tiraboschi wrote:
>     Is there a reason why it has to be exactly replica 3?
>
>
> To have a valid quorum having the system being able to decide witch is
> the right and safe copy avoiding an issue called split brain.
> Under certain circumstances/issues (network issue, hosts down or
> whatever could happen) the data on different replica could diverge: if
> you have two and just two different hosts that claim each other
that its
> copy is the right one there is no way to automatically take the right
> decision. Having three hosts and setting the quorum according to that
> solves/mitigates the issue.


Thanks for the explanation. I do understand the problem but since
I'm somewhat limited in my hardware options is there a way to
override this requirement? Meaning if I change the checks for
replica 3 in the installation scripts does something else fail on
the way?

In my case coherence checks would come from outside the storage and
vm host setup and fencing would be applied appropriately.

I would very much appreciate it if the particulars of the storage
setup could be either selected from a list of possibilities or be
ignored and just a warning be issued that this setup is not recommended.

Thanks!
Richard


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