[Gluster-users] Default quorum for 2 way replication

[Pranith Kumar Karampuri]

On 03/04/2016 05:47 PM, Bipin Kunal wrote:
> HI Pranith,
>
> Thanks for starting this mail thread.
>
> Looking from a user perspective most important is to get a "good copy"
> of data.  I agree that people use replication for HA but having stale
> data with HA will not have any value.
> So I will suggest to make auto quorum as default configuration even
> for 2-way replication.
>
> If user is willing to lose data at the cost of HA, he always have
> option disable it. But default preference should be data and its
> integrity.

That is the point. There is an illusion of choice between Data integrity 
and HA. But we are not *really* giving HA, are we? HA will be there only 
if second brick in the replica pair goes down. In your typical 
deployment, we can't really give any guarantees about what brick will go 
down when. So I am not sure if we can consider it as HA. But I would 
love to hear what others have to say about this as well. If majority of 
users say they need it to be auto, you will definitely see a patch :-).

Pranith
>
> Thanks,
> Bipin Kunal
>
> On Fri, Mar 4, 2016 at 5:43 PM, Ravishankar N <ravishankar at redhat.com> wrote:
>> On 03/04/2016 05:26 PM, Pranith Kumar Karampuri wrote:
>>> hi,
>>>       So far default quorum for 2-way replication is 'none' (i.e.
>>> files/directories may go into split-brain) and for 3-way replication and
>>> arbiter based replication it is 'auto' (files/directories won't go into
>>> split-brain). There are requests to make default as 'auto' for 2-way
>>> replication as well. The line of reasoning is that people value data
>>> integrity (files not going into split-brain) more than HA (operation of
>>> mount even when bricks go down). And admins should explicitly change it to
>>> 'none' when they are fine with split-brains in 2-way replication. We were
>>> wondering if you have any inputs about what is a sane default for 2-way
>>> replication.
>>>
>>> I like the default to be 'none'. Reason: If we have 'auto' as quorum for
>>> 2-way replication and first brick dies, there is no HA.
>>
>>
>> +1.  Quorum does not make sense when there are only 2 parties. There is no
>> majority voting. Arbiter volumes are a better option.
>> If someone wants some background, please see 'Client quorum' and 'Replica 2
>> and Replica 3 volumes' section of
>> http://gluster.readthedocs.org/en/latest/Administrator%20Guide/arbiter-volumes-and-quorum/
>>
>> -Ravi
>>
>>> If users are fine with it, it is better to use plain distribute volume
>>> rather than replication with quorum as 'auto'. What are your thoughts on the
>>> matter? Please guide us in the right direction.
>>>
>>> Pranith
>>
>>