Gluster users - Jul 2015 - 3.7 Arbiter and/or quorum

On 07/15/2015 09:22 PM, Scott Harvanek wrote:
> I saw Ravi mention something earlier about the new arbiter volumes in 3.7
>
> - Can you run a arbiter 3.7 server volume with 3.6 clients?  Or does 
> this not work?
>
>
Unfortunately, no. This is because the logic for the feature is mostly 
in the AFR translator which is loaded on the client process (with some 
minor logic in the arbiter translator loaded on the brick process). So 
both clients and servers need to be 3.7.

> Quorum question -
>
> - 3.6 server and clients, replica 2, however there's three+ servers in 
> the cluster ( gluster pool list ).  If one of the replicas fail is 
> quorum maintained via the other servers in the cluster even though 
> they are not part of the volume?
>
That would depend on what type of quorum is enabled (client or server 
side). Each type has a different impact. You can look for the meaning of 
cluster.quorum-type, cluster.quorum-count (these are client side quorum 
options, applicable only to replicate volumes) and 
cluster.server-quorum-type, cluster.server-quorum-ratio (these are 
server side quorum options; they are not specific to replicate volumes) 
in 'gluster volume set help`.

HTH,
Ravi

Using the virt group which does-

cluster.quorum-type: auto
cluster.server-quorum-type: server

And from my understanding this means that quorum enforcement is enabled, 
and that it's brick related so if I only have two bricks then I cannot 
achieve 51% and split brain is likely even with a third node in the 
pool.  If I move to fixed 1, then the likelihood of splitbrain is high.

So what do I do here, get a fourth node and do distributed replicated?  
Trying to find the best performance option while minimizing split brain 
potential and I'm stuck with 3.6 clients ( RHEV-H ) so the 
aforementioned arbiter is out, Replica 3 just seems to be a pig on the 
client side due to the triple write.

-- 
Scott H.



> Ravishankar N <mailto:ravishankar at redhat.com>
> July 15, 2015 at 1:09 PM
>
>
> On 07/15/2015 09:22 PM, Scott Harvanek wrote:
>> I saw Ravi mention something earlier about the new arbiter volumes in 
>> 3.7
>>
>> - Can you run a arbiter 3.7 server volume with 3.6 clients?  Or does 
>> this not work?
>>
>>
>
> Unfortunately, no. This is because the logic for the feature is mostly 
> in the AFR translator which is loaded on the client process (with some 
> minor logic in the arbiter translator loaded on the brick process). So 
> both clients and servers need to be 3.7.
>
>
>> Quorum question -
>>
>> - 3.6 server and clients, replica 2, however there's three+ servers
>> in the cluster ( gluster pool list ).  If one of the replicas fail is 
>> quorum maintained via the other servers in the cluster even though 
>> they are not part of the volume?
>>
> That would depend on what type of quorum is enabled (client or server 
> side). Each type has a different impact. You can look for the meaning 
> of cluster.quorum-type, cluster.quorum-count (these are client side 
> quorum options, applicable only to replicate volumes) and 
> cluster.server-quorum-type, cluster.server-quorum-ratio (these are 
> server side quorum options; they are not specific to replicate 
> volumes) in 'gluster volume set help`.
>
> HTH,
> Ravi
> Scott Harvanek <mailto:scott.harvanek at login.com>
> July 15, 2015 at 11:52 AM
> I saw Ravi mention something earlier about the new arbiter volumes in 3.7
>
> - Can you run a arbiter 3.7 server volume with 3.6 clients?  Or does 
> this not work?
>
>
> Quorum question -
>
> - 3.6 server and clients, replica 2, however there's three+ servers in 
> the cluster ( gluster pool list ).  If one of the replicas fail is 
> quorum maintained via the other servers in the cluster even though 
> they are not part of the volume?
>
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On Wed, 2015-07-15 at 22:39 +0530, Ravishankar N wrote:
> 
> On 07/15/2015 09:22 PM, Scott Harvanek wrote:
> > I saw Ravi mention something earlier about the new arbiter volumes in
3.7
> >
> > - Can you run a arbiter 3.7 server volume with 3.6 clients?  Or does 
> > this not work?
> >
> >
> 
> Unfortunately, no. This is because the logic for the feature is mostly 
> in the AFR translator which is loaded on the client process (with some 
> minor logic in the arbiter translator loaded on the brick process). So 
> both clients and servers need to be 3.7.
Is there any harm in running 3.6 clients with a 3.7 cluster?

We're currently running 3.6.3 and if we upgrade the cluster to 3.7 at
some point it would be nice to know whether we can upgrade the clients
in a separate step (given that we have a reasonable number of them).

-- 
Cheers,
Kingsley.