On Wed, Sep 9, 2015 at 10:49 AM, Jorick Astrego <j.astrego@netbulae.eu> wrote:


On 09/09/2015 10:14 AM, Richard Neuboeck wrote:
> 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
>
>
As a side question, in Glusterfs 3.7 there is an "AFR arbiter volume"
(http://gluster.readthedocs.org/en/release-3.7.0-1/Features/afr-arbiter-volumes/)
that will only contain the metadata.

Will ovirt support this in 3.6?

Not explicitly and I never tried it with hosted-engine but I suspect it works as far it will report  replica level = 3.

By the way you can save disk space on the third host but you still need three hosts.


Kind regards,

Jorick Astrego




Met vriendelijke groet, With kind regards,

Jorick Astrego

Netbulae Virtualization Experts
Tel: 053 20 30 270 info@netbulae.eu Staalsteden 4-3A KvK 08198180
Fax: 053 20 30 271 www.netbulae.eu 7547 TA Enschede BTW NL821234584B01



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