[Gluster-users] Conflict resolution

[David Cunningham]

Hi Strahil and Ravi,

Thank you very much for your replies, that makes sense.



On Thu, 21 Oct 2021 at 03:25, Ravishankar N <ravishankar.n at pavilion.io>
wrote:

> Hi David,
>
> On Wed, Oct 20, 2021 at 6:23 AM David Cunningham <
> dcunningham at voisonics.com> wrote:
>
>> Hello,
>>
>> I've a few questions about conflict resolution in a net-split scenario:
>>
>> 1. What are the default values for cluster.server-quorum-type and
>> cluster.server-quorum-ratio? (at the moment "gluster volume info gvol0"
>> does not report either)
>>
>> $gluster volume get gvol0 cluster.server-quorum-type
> $gluster volume get all cluster.server-quorum-ratio
>
>
>
>> 2. If there are 3 mirrored nodes and cluster.server-quorum-ratio is 50,
>> and node1 and node2 are net-split from node3, then am I right in thinking
>> that the volume on node3 will automatically shut down and prevent access
>> thus preventing a conflict?
>>
>> Yes, the glusterd on node 3 will kill the brick processes on that node.
>
>
>> 3. If there are 2 mirrored nodes and a net-split happens and
>> cluster.server-quorum-ratio is 50 then:
>> a) If existing file A is changed on node1 and node2 then the file will
>> enter net-split state, right?
>>
>
> Yes, for 2 node setups, you must set the ratio to 51% to avoid this. I'm
> assuming that the 'changing' that you refer to is happening via fuse mounts
> on each of these nodes.
>
>
>> b) If existing file B is changed on node1 but not node2 then will the
>> file enter a net-split state?
>>
> No.
>
>
>> c) If new file C is written on node1 but not node2 then will the file
>> enter a net-split state?
>>
>> No.
>
>
>> 4. Is the outcome of conflict resolution at a file level the same whether
>> node3 is a full replica or just an arbiter?
>>
>> server quorum feature is not related to replication. It really is a
> glusterd thing and doesn't really help prevent split-brains, because
> split-brains are caused by failed I/Os from clients and the clients can be
> mounted even outside the storage pool. What you need to ensure is
> that cluster.quorum-type (which is 'client' quorum) is set to auto for
> replica 3 and arbiter. It already is by default. See
> https://docs.gluster.org/en/latest/Administrator-Guide/arbiter-volumes-and-quorum/#split-brains-in-replica-volumes
> for more info.
>
> -Ravi
>
>> Thank you very much for any advice,
>>
>> --
>> David Cunningham, Voisonics Limited
>> http://voisonics.com/
>> USA: +1 213 221 1092
>> New Zealand: +64 (0)28 2558 3782
>> ________
>>
>>
>>
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>

-- 
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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