[ovirt-users] hyperconverged question

Fri Sep 1 16:09:15 UTC 2017

@Kasturi - Looks good now. Cluster showed down for a moment but VM's stayed
up in their appropriate places. Thanks!

< Anyone on this list please feel free to correct my response to Jim if its
wrong>

@ Jim - If you can share your gluster volume info / status I can confirm
(to the best of my knowledge). From my understanding, If you setup the
volume with something like 'gluster volume set <vol> group virt' this will
configure some quorum options as well, Ex: http://i.imgur.com/Mya4N5o.png

While, yes, you are configured for arbiter node you're still losing quorum
by dropping from 2 -> 1. You would need 4 node with 1 being arbiter to
configure quorum which is in effect 3 writable nodes and 1 arbiter. If one
gluster node drops, you still have 2 up. Although in this case, you
probably wouldnt need arbiter at all

If you are configured, you can drop quorum settings and just let arbiter
run since you're not using arbiter node in your VM cluster part (I
believe), just storage cluster part. When using quorum, you need > 50% of
the cluster being up at one time. Since you have 3 nodes with 1 arbiter,
you're actually losing 1/2 which == 50 which == degraded / hindered gluster

Again, this is to the best of my knowledge based on other quorum backed
software....and this is what I understand from testing with gluster and
ovirt thus far

On Fri, Sep 1, 2017 at 11:53 AM, Jim Kusznir <jim at palousetech.com> wrote:

> Huh...Ok., how do I convert the arbitrar to full replica, then?  I was
> misinformed when I created this setup.  I thought the arbitrator held
> enough metadata that it could validate or refudiate  any one replica (kinda
> like the parity drive for a RAID-4 array).  I was also under the impression
> that one replica  + Arbitrator is enough to keep the array online and
> functional.
>
> --Jim
>
> On Fri, Sep 1, 2017 at 5:22 AM, Charles Kozler <ckozleriii at gmail.com>
> wrote:
>
>> @ Jim - you have only two data volumes and lost quorum. Arbitrator only
>> stores metadata, no actual files. So yes, you were running in degraded mode
>> so some operations were hindered.
>>
>> @ Sahina - Yes, this actually worked fine for me once I did that.
>> However, the issue I am still facing, is when I go to create a new gluster
>> storage domain (replica 3, hyperconverged) and I tell it "Host to use" and
>> I select that host. If I fail that host, all VMs halt. I do not recall this
>> in 3.6 or early 4.0. This to me makes it seem like this is "pinning" a node
>> to a volume and vice versa like you could, for instance, for a singular
>> hyperconverged to ex: export a local disk via NFS and then mount it via
>> ovirt domain. But of course, this has its caveats. To that end, I am using
>> gluster replica 3, when configuring it I say "host to use: " node 1, then
>> in the connection details I give it node1:/data. I fail node1, all VMs
>> halt. Did I miss something?
>>
>> On Fri, Sep 1, 2017 at 2:13 AM, Sahina Bose <sabose at redhat.com> wrote:
>>
>>> To the OP question, when you set up a gluster storage domain, you need
>>> to specify backup-volfile-servers=<server2>:<server3> where server2 and
>>> server3 also have bricks running. When server1 is down, and the volume is
>>> mounted again - server2 or server3 are queried to get the gluster volfiles.
>>>
>>> @Jim, if this does not work, are you using 4.1.5 build with libgfapi
>>> access? If not, please provide the vdsm and gluster mount logs to analyse
>>>
>>> If VMs go to paused state - this could mean the storage is not
>>> available. You can check "gluster volume status <volname>" to see if
>>> atleast 2 bricks are running.
>>>
>>> On Fri, Sep 1, 2017 at 11:31 AM, Johan Bernhardsson <johan at kafit.se>
>>> wrote:
>>>
>>>> If gluster drops in quorum so that it has less votes than it should it
>>>> will stop file operations until quorum is back to normal.If i rember it
>>>> right you need two bricks to write for quorum to be met and that the
>>>> arbiter only is a vote to avoid split brain.
>>>>
>>>>
>>>> Basically what you have is a raid5 solution without a spare. And when
>>>> one disk dies it will run in degraded mode. And some raid systems will stop
>>>> the raid until you have removed the disk or forced it to run anyway.
>>>>
>>>> You can read up on it here: https://gluster.readthed
>>>> ocs.io/en/latest/Administrator%20Guide/arbiter-volumes-and-quorum/
>>>>
>>>> /Johan
>>>>
>>>> On Thu, 2017-08-31 at 22:33 -0700, Jim Kusznir wrote:
>>>>
>>>> Hi all:
>>>>
>>>> Sorry to hijack the thread, but I was about to start essentially the
>>>> same thread.
>>>>
>>>> I have a 3 node cluster, all three are hosts and gluster nodes (replica
>>>> 2 + arbitrar).  I DO have the mnt_options=backup-volfile-servers= set:
>>>>
>>>> storage=192.168.8.11:/engine
>>>> mnt_options=backup-volfile-servers=192.168.8.12:192.168.8.13
>>>>
>>>> I had an issue today where 192.168.8.11 went down.  ALL VMs immediately
>>>> paused, including the engine (all VMs were running on host2:192.168.8.12).
>>>> I couldn't get any gluster stuff working until host1 (192.168.8.11) was
>>>> restored.
>>>>
>>>> What's wrong / what did I miss?
>>>>
>>>> (this was set up "manually" through the article on setting up
>>>> self-hosted gluster cluster back when 4.0 was new..I've upgraded it to 4.1
>>>> since).
>>>>
>>>> Thanks!
>>>> --Jim
>>>>
>>>>
>>>> On Thu, Aug 31, 2017 at 12:31 PM, Charles Kozler <ckozleriii at gmail.com>
>>>> wrote:
>>>>
>>>> Typo..."Set it up and then failed that **HOST**"
>>>>
>>>> And upon that host going down, the storage domain went down. I only
>>>> have hosted storage domain and this new one - is this why the DC went down
>>>> and no SPM could be elected?
>>>>
>>>> I dont recall this working this way in early 4.0 or 3.6
>>>>
>>>> On Thu, Aug 31, 2017 at 3:30 PM, Charles Kozler <ckozleriii at gmail.com>
>>>> wrote:
>>>>
>>>> So I've tested this today and I failed a node. Specifically, I setup a
>>>> glusterfs domain and selected "host to use: node1". Set it up and then
>>>> failed that VM
>>>>
>>>> However, this did not work and the datacenter went down. My engine
>>>> stayed up, however, it seems configuring a domain to pin to a host to use
>>>> will obviously cause it to fail
>>>>
>>>> This seems counter-intuitive to the point of glusterfs or any redundant
>>>> storage. If a single host has to be tied to its function, this introduces a
>>>> single point of failure
>>>>
>>>> Am I missing something obvious?
>>>>
>>>> On Thu, Aug 31, 2017 at 9:43 AM, Kasturi Narra <knarra at redhat.com>
>>>> wrote:
>>>>
>>>> yes, right.  What you can do is edit the hosted-engine.conf file and
>>>> there is a parameter as shown below [1] and replace h2 and h3 with your
>>>> second and third storage servers. Then you will need to restart
>>>> ovirt-ha-agent and ovirt-ha-broker services in all the nodes .
>>>>
>>>> [1] 'mnt_options=backup-volfile-servers=<h2>:<h3>'
>>>>
>>>> On Thu, Aug 31, 2017 at 5:54 PM, Charles Kozler <ckozleriii at gmail.com>
>>>> wrote:
>>>>
>>>> Hi Kasturi -
>>>>
>>>> Thanks for feedback
>>>>
>>>> > If cockpit+gdeploy plugin would be have been used then that would
>>>> have automatically detected glusterfs replica 3 volume created during
>>>> Hosted Engine deployment and this question would not have been asked
>>>>
>>>> Actually, doing hosted-engine --deploy it too also auto detects
>>>> glusterfs.  I know glusterfs fuse client has the ability to failover
>>>> between all nodes in cluster, but I am still curious given the fact that I
>>>> see in ovirt config node1:/engine (being node1 I set it to in hosted-engine
>>>> --deploy). So my concern was to ensure and find out exactly how engine
>>>> works when one node goes away and the fuse client moves over to the other
>>>> node in the gluster cluster
>>>>
>>>> But you did somewhat answer my question, the answer seems to be no (as
>>>> default) and I will have to use hosted-engine.conf and change the parameter
>>>> as you list
>>>>
>>>> So I need to do something manual to create HA for engine on gluster?
>>>> Yes?
>>>>
>>>> Thanks so much!
>>>>
>>>> On Thu, Aug 31, 2017 at 3:03 AM, Kasturi Narra <knarra at redhat.com>
>>>> wrote:
>>>>
>>>> Hi,
>>>>
>>>>    During Hosted Engine setup question about glusterfs volume is being
>>>> asked because you have setup the volumes yourself. If cockpit+gdeploy
>>>> plugin would be have been used then that would have automatically detected
>>>> glusterfs replica 3 volume created during Hosted Engine deployment and this
>>>> question would not have been asked.
>>>>
>>>>    During new storage domain creation when glusterfs is selected there
>>>> is a feature called 'use managed gluster volumes' and upon checking this
>>>> all glusterfs volumes managed will be listed and you could choose the
>>>> volume of your choice from the dropdown list.
>>>>
>>>>     There is a conf file called /etc/hosted-engine/hosted-engine.conf
>>>> where there is a parameter called backup-volfile-servers="h1:h2" and if one
>>>> of the gluster node goes down engine uses this parameter to provide ha /
>>>> failover.
>>>>
>>>>  Hope this helps !!
>>>>
>>>> Thanks
>>>> kasturi
>>>>
>>>>
>>>>
>>>> On Wed, Aug 30, 2017 at 8:09 PM, Charles Kozler <ckozleriii at gmail.com>
>>>> wrote:
>>>>
>>>> Hello -
>>>>
>>>> I have successfully created a hyperconverged hosted engine setup
>>>> consisting of 3 nodes - 2 for VM's and the third purely for storage. I
>>>> manually configured it all, did not use ovirt node or anything. Built the
>>>> gluster volumes myself
>>>>
>>>> However, I noticed that when setting up the hosted engine and even when
>>>> adding a new storage domain with glusterfs type, it still asks for
>>>> hostname:/volumename
>>>>
>>>> This leads me to believe that if that one node goes down (ex:
>>>> node1:/data), then ovirt engine wont be able to communicate with that
>>>> volume because its trying to reach it on node 1 and thus, go down
>>>>
>>>> I know glusterfs fuse client can connect to all nodes to provide
>>>> failover/ha but how does the engine handle this?
>>>>
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