[Gluster-devel] [ovirt-users] Can we debug some truths/myths/facts about hosted-engine and gluster?
Vijay Bellur
vbellur at redhat.com
Tue Jul 22 01:28:54 UTC 2014
On 07/21/2014 05:09 AM, Pranith Kumar Karampuri wrote:
>
> 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.
>
Does hosted engine perform deletion & re-creation of file
<uuid>/ha_agent/hosted-engine.metadata in some operational sequence? In
such a case, if this file is accessed by a stale gfid, ESTALE is possible.
I see references to 2 hosted engines being operational in the bug report
and that makes me wonder if this is a likely scenario?
I am also curious to understand why NFS was chosen as the access method
to the gluster volume. Isn't FUSE based access a possibility here?
-Vijay
More information about the Gluster-devel
mailing list