[ovirt-users] Affinity

[Doron Fediuck]

On 05/01/15 11:26, Koen Vanoppen wrote:
> Thanks for your reply. But I maybe explained it badly... All the 4
> hypervisors are in the same Datacenter on oVirt. But they are
> physically in a different datacenter.
> That is why I want to force them to run on a different hypervisor. IF
> 1 physical datacenter would go down (electricity power failure or
> whatever) At least one VM will continue to run.
>
> 2015-01-05 10:21 GMT+01:00 Doron Fediuck <dfediuck at redhat.com
> <mailto:dfediuck at redhat.com>>:
>
>
>     On 05/01/15 10:54, Koen Vanoppen wrote:
>>     Hi All,
>>
>>     First of all, let me say a Happy New Year with all the best wishes!!
>>
>>     Now, let's get down to business :-).
>>
>>     I would lik eto implement the Affinity option in our datacenter.
>>     I already activated it, put the 2 vms in it and set in on
>>     negative so they won't run together on the same hypervisor. Now,
>>     the question...
>>     Is there a way I can force the VM's so they will run on a
>>     hypervisor that is not in the same datacenter? We have this;
>>
>>     Hyp1 -> Datacenter1
>>     Hyp2 -> Datacenter2
>>     Hyp3 -> Datacenter1
>>     Hyp4 -> Datacenter2
>>
>>     For the moment they run on a different Hypervisor, but they are
>>     in the same Datacenter. I can manually now move them to the other
>>     one, but I would like this that oVirt manages this...
>>     Is this possible...?
>>
>>     Kind regards,
>>
>>     Koen
>>
>>
>     Hi Koen.
>
>     VMs cannot move between data centers while still running.
>     Just to provide some basic concepts in terms of hierarchy, we have:
>
>     Data-Center1
>     |
>     |\ Cluster A
>     | |
>     | |\ Host (a)
>     | |\ Host (b)
>     |
>     |\ Cluster B
>     | |
>     | |\ Host (c)
>     | |\ Host (d)
>     | |\ Host (e)
>
>     Data-Center2
>     |
>     |\ Cluster A
>     | |
>     | |\ Host (f)
>     |
>     |\ Cluster B
>     | |
>     | |\ Host (g)
>     | |\ Host (h)
>     | |\ Host (i)
>
>     As you can see, a host may be a part of a single cluster and a VM
>     will run on one of the hosts. Live migration can be done between
>     hosts of the same cluster. The only way to move VM between clusters
>     and DCs are when the VM is down, in a manual way.
>
>     So Affinity works in the cluster level, and the rules are valid for a
>     specific cluster who currently owns the VM.
>     In your case if Hyp1 and Hyp3 belong to the same cluster, the affinity
>     rules will apply every time you start or migrate a VM. However,
>     there's
>     no rule which is valid for Datacenter1 and Datacenter2.
>
>     HTH,
>     Doron
>
>

Koen,
this is clear now.
Currently affinity applies to VMs only. For 3.6 we're planning "pin to
hosts"
which will allow you to pin VMs to a group of hosts, such as Datacenter1
hosts
in your case. Until 3.6 will be available (which will take a while), you
can consider
writing a filter module for the ovirt scheduler. Let me know if you need
more
details.

Doron
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