[ovirt-users] storage redundancy in Ovirt

[Dan Yasny]

On Sun, Apr 16, 2017 at 11:15 PM, Konstantin Raskoshnyi <konrasko at gmail.com>
wrote:

> Fence agent under each node?
>

When you configure a host, there's the power management tab, where you need
to enter the bmc details for the host. If you don't have fencing enabled,
how do you expect the system to make sure a host running a service is
actually down (and it is safe to start HA services elsewhere), and not, for
example, just unreachable by the engine? How do you avoid a splitbraid ->
SBA ?


>
> On Sun, Apr 16, 2017 at 8:14 PM Dan Yasny <dyasny at gmail.com> wrote:
>
>> On Sun, Apr 16, 2017 at 11:13 PM, Konstantin Raskoshnyi <
>> konrasko at gmail.com> wrote:
>>
>>> "Corner cases"?
>>> I tried to simulate crash of SPM server and ovirt kept trying to
>>> reistablished connection to the failed node.
>>>
>>
>> Did you configure fencing?
>>
>>
>>>
>>>
>>> On Sun, Apr 16, 2017 at 8:10 PM Dan Yasny <dyasny at gmail.com> wrote:
>>>
>>>> On Sun, Apr 16, 2017 at 7:29 AM, Nir Soffer <nsoffer at redhat.com> wrote:
>>>>
>>>>> On Sun, Apr 16, 2017 at 2:05 PM Dan Yasny <dyasny at redhat.com> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Apr 16, 2017 7:01 AM, "Nir Soffer" <nsoffer at redhat.com> wrote:
>>>>>>
>>>>>> On Sun, Apr 16, 2017 at 4:17 AM Dan Yasny <dyasny at gmail.com> wrote:
>>>>>>
>>>>>>> When you set up a storage domain, you need to specify a host to
>>>>>>> perform the initial storage operations, but once the SD is defined, it's
>>>>>>> details are in the engine database, and all the hosts get connected to it
>>>>>>> directly. If the first host you used to define the SD goes down, all other
>>>>>>> hosts will still remain connected and work. SPM is an HA service, and if
>>>>>>> the current SPM host goes down, SPM gets started on another host in the DC.
>>>>>>> In short, unless your actual NFS exporting host goes down, there is no
>>>>>>> outage.
>>>>>>>
>>>>>>
>>>>>> There is no storage outage, but if you shutdown the spm host, the spm
>>>>>> host
>>>>>> will not move to a new host until the spm host is online again, or
>>>>>> you confirm
>>>>>> manually that the spm host was rebooted.
>>>>>>
>>>>>>
>>>>>> In a properly configured setup the SBA should take care of that.
>>>>>> That's the whole point of HA services
>>>>>>
>>>>>
>>>>> In some cases like power loss or hardware failure, there is no way to
>>>>> start
>>>>> the spm host, and the system cannot recover automatically.
>>>>>
>>>>
>>>> There are always corner cases, no doubt. But in a normal situation.
>>>> where an SPM host goes down because of a hardware failure, it gets fenced,
>>>> other hosts contend for SPM and start it. No surprises there.
>>>>
>>>>
>>>>>
>>>>> Nir
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>> Nir
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> On Sat, Apr 15, 2017 at 1:53 PM, Konstantin Raskoshnyi <
>>>>>>> konrasko at gmail.com> wrote:
>>>>>>>
>>>>>>>> Hi Fernando,
>>>>>>>> I see each host has direct connection nfs mount, but yes, if main
>>>>>>>> host to which I connected nfs storage going down the storage becomes
>>>>>>>> unavailable and all vms are down
>>>>>>>>
>>>>>>>>
>>>>>>>> On Sat, Apr 15, 2017 at 10:37 AM FERNANDO FREDIANI <
>>>>>>>> fernando.frediani at upx.com> wrote:
>>>>>>>>
>>>>>>>>> Hello Konstantin.
>>>>>>>>>
>>>>>>>>> That doesn`t make much sense make a whole cluster depend on a
>>>>>>>>> single host. From what I know any host talk directly to NFS Storage Array
>>>>>>>>> or whatever other Shared Storage you have.
>>>>>>>>> Have you tested that host going down if that affects the other
>>>>>>>>> with the NFS mounted directlly in a NFS Storage array ?
>>>>>>>>>
>>>>>>>>> Fernando
>>>>>>>>>
>>>>>>>>> 2017-04-15 12:42 GMT-03:00 Konstantin Raskoshnyi <
>>>>>>>>> konrasko at gmail.com>:
>>>>>>>>>
>>>>>>>>>> In ovirt you have to attach storage through specific host.
>>>>>>>>>> If host goes down storage is not available.
>>>>>>>>>>
>>>>>>>>>> On Sat, Apr 15, 2017 at 7:31 AM FERNANDO FREDIANI <
>>>>>>>>>> fernando.frediani at upx.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> Well, make it not go through host1 and dedicate a storage server
>>>>>>>>>>> for running NFS and make both hosts connect to it.
>>>>>>>>>>> In my view NFS is much easier to manage than any other type of
>>>>>>>>>>> storage, specially FC and iSCSI and performance is pretty much the same, so
>>>>>>>>>>> you won`t get better results other than management going to other type.
>>>>>>>>>>>
>>>>>>>>>>> Fernando
>>>>>>>>>>>
>>>>>>>>>>> 2017-04-15 5:25 GMT-03:00 Konstantin Raskoshnyi <
>>>>>>>>>>> konrasko at gmail.com>:
>>>>>>>>>>>
>>>>>>>>>>>> Hi guys,
>>>>>>>>>>>> I have one nfs storage,
>>>>>>>>>>>> it's connected through host1.
>>>>>>>>>>>> host2 also has access to it, I can easily migrate vms between
>>>>>>>>>>>> them.
>>>>>>>>>>>>
>>>>>>>>>>>> The question is - if host1 is down - all infrastructure is
>>>>>>>>>>>> down, since all traffic goes through host1,
>>>>>>>>>>>> is there any way in oVirt to use redundant storage?
>>>>>>>>>>>>
>>>>>>>>>>>> Only glusterfs?
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks
>>>>>>>>>>>>
>>>>>>>>>>>>
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>>>>>>>>>
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