[Gluster-devel] [ovirt-users] Can we debug some truths/myths/facts about hosted-engine and gluster?
Pranith Kumar Karampuri
pkarampu at redhat.com
Mon Jul 21 09:09:08 UTC 2014
On 07/21/2014 02:08 PM, Jiri Moskovcak wrote:
> On 07/19/2014 08:58 AM, Pranith Kumar Karampuri wrote:
>>
>> On 07/19/2014 11:25 AM, Andrew Lau wrote:
>>>
>>>
>>> On Sat, Jul 19, 2014 at 12:03 AM, Pranith Kumar Karampuri
>>> <pkarampu at redhat.com <mailto:pkarampu at redhat.com>> wrote:
>>>
>>>
>>> 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
>>>
>>>
>>> Unfortunately, I don't have the logs for that setup any more.. I'll
>>> try replicate when I get a chance. If I understand the comment from
>>> the BZ, I don't think it's a gluster bug per-say, more just how
>>> gluster does its replication.
>> hi Andrew,
>> Thanks for that. I couldn't come to any conclusions because no
>> logs were available. It is unlikely that self-heal is involved because
>> there were no bricks going down/up according to the bug description.
>>
>
> Hi,
> I've never had such setup, I guessed problem with gluster based on
> "OSError: [Errno 116] Stale file handle:" which happens when the file
> opened by application on client gets removed on the server. I'm pretty
> sure we (hosted-engine) don't remove that file, so I think it's some
> gluster magic moving the data around...
Hi,
Without bricks going up/down or there are new bricks added data is not
moved around by gluster unless a file operation comes to gluster. So I
am still not sure why this happened.
Pranith
>
> --Jirka
>
>> 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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>>>
>>>
>>
>
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