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

[Pranith Kumar Karampuri]

On 07/18/2014 05:43 PM, Andrew Lau wrote:
>
> On Fri, Jul 18, 2014 at 10:06 PM, Vijay Bellur <vbellur at redhat.com 
> <mailto:vbellur at redhat.com>> wrote:
>
>     [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 :).
>
>
> I'm not sure how useful this is, but Jiri Moskovcak tracked this down 
> in an off list message.
>
> Message Quote:
>
> ==
>
> We were able to track it down to this (thanks Andrew for providing the 
> testing setup):
>
> -b686-4363-bb7e-dba99e5789b6/ha_agent service_type=hosted-engine'
> Traceback (most recent call last):
> File 
> "/usr/lib/python2.6/site-packages/ovirt_hosted_engine_ha/broker/listener.py", 
> line 165, in handle
>   response = "success " + self._dispatch(data)
> File 
> "/usr/lib/python2.6/site-packages/ovirt_hosted_engine_ha/broker/listener.py", 
> line 261, in _dispatch
>   .get_all_stats_for_service_type(**options)
> File 
> "/usr/lib/python2.6/site-packages/ovirt_hosted_engine_ha/broker/storage_broker.py", 
> line 41, in get_all_stats_for_service_type
>   d = self.get_raw_stats_for_service_type(storage_dir, service_type)
> File 
> "/usr/lib/python2.6/site-packages/ovirt_hosted_engine_ha/broker/storage_broker.py", 
> line 74, in get_raw_stats_for_service_type
>   f = os.open(path, direct_flag | os.O_RDONLY)
> OSError: [Errno 116] Stale file handle: 
> '/rhev/data-center/mnt/localhost:_mnt_hosted-engine/c898fd2a-b686-4363-bb7e-dba99e5789b6/ha_agent/hosted-engine.metadata'
Andrew/Jiri,
         Would it be possible to post gluster logs of both the mount and 
bricks on the bz? I can take a look at it once. If I gather nothing then 
probably I will ask for your help in re-creating the issue.

Pranith

>
> It's definitely connected to the storage which leads us to the 
> gluster, I'm not very familiar with the gluster so I need to check 
> this with our gluster gurus.
>
> ==
>
>     Thanks,
>     Vijay
>
>
>
>
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