[ovirt-users] Can we debug some truths/myths/facts about hosted-engine and gluster?

[Vijay Bellur]

[Adding gluster-devel]

On 07/18/2014 05:20 PM, Andrew Lau wrote:
> Hi all,
>
> As most of you have got hints from previous messages, hosted engine
> won't work on gluster . A quote from BZ1097639
>
> "Using hosted engine with Gluster backed storage is currently something
> we really warn against.
>
>
> I think this bug should be closed or re-targeted at documentation, because there is nothing we can do here. Hosted engine assumes that all writes are atomic and (immediately) available for all hosts in the cluster. Gluster violates those assumptions.
> ​"
I tried going through BZ1097639 but could not find much detail with 
respect to gluster there.

A few questions around the problem:

1. Can somebody please explain in detail the scenario that causes the 
problem?

2. Is hosted engine performing synchronous writes to ensure that writes 
are durable?

Also, if there is any documentation that details the hosted engine 
architecture that would help in enhancing our understanding of its 
interactions with gluster.

> ​
>
> Now my question, does this theory prevent a scenario of perhaps
> something like a gluster replicated volume being mounted as a glusterfs
> filesystem and then re-exported as the native kernel NFS share for the
> hosted-engine to consume? It could then be possible to chuck ctdb in
> there to provide a last resort failover solution. I have tried myself
> and suggested it to two people who are running a similar setup. Now
> using the native kernel NFS server for hosted-engine and they haven't
> reported as many issues. Curious, could anyone validate my theory on this?
>

If we obtain more details on the use case and obtain gluster logs from 
the failed scenarios, we should be able to understand the problem 
better. That could be the first step in validating your theory or 
evolving further recommendations :).

Thanks,
Vijay