[ovirt-users] Is this kind of VM replication possible using oVirt Schedular

[kausik pal]

hi Gilad/Martin,

Please let me know if you need any further clarifications from my side.

Thanks
Kausik


On Fri, Jun 27, 2014 at 3:18 PM, kausik pal <kausikpal.1 at gmail.com> wrote:

> Hi Gilad/Martin,
>
> Thanks for the reply.
>
> Let me explain the scenario in details:-
>
> Each Host would have local filesystems and can be integrated with oVirt as
> POSIX filesystems storage.
>
> Assume each server can run maximum 6 VMs simultaneously(due to memory/CPU
> constraints) and we have configured 5 hosts (Node1, Node2....Node5).
>
> In the beginning the 5 hosts are being configured in the oVirt engine and
> there is no VM.
>
> Now I create the first VM named VM1 and place it in Node1, from this point
> oVirt Schedular would decide which other host it would put the replica on.
> This replica VM1 will be in passive state in another host (Node 2 as per
> diagram). The same procedure would apply on the other created VMs as well.
>
> The role of the oVirt scheduler would be to optimize the placement of VMs
> in such a way that we can maximize the number of VMs availability in case
> of host(s) failure. Also it should replicate the delta updates to
> corresponding passive VMs.
>
> As per the scenario in a perfect condition 4 VMs are running in each host
> providing scope for running 2 extra VMs(maximum 6)in case of other host
> failures.The underlying local storage have kept 4 extra VMs (QCOW2 disks
> and config files) from different hosts in addition to the 4 VM disk files
> for the running VMs.
>
> Due to some reason Node2 and Node4 have failed, now the replicated passive
> VMs for the failed nodes will be started on the remaining nodes. In this
> case most of the VMs were able to start in different node except VM7 and
> VM14 as those VMs don't have replicas available in the other running nodes.
>
> The maximum availability of the VMs can be calculated using the following
> formula:-
>
> *Total No. of VMs running after node failure = ((Total No. of Nodes) -
> (No. of failed Nodes)) * (Max. No. of VMs that can run per Node)*
>
> The HA VM reservation is an excellent feature no doubt, but I think its
> only applicable if you have a shared storage underlying(NFS,SAN,Gluster
> etc..).(Correct me if I'm wrong)
>
> And yes GlusterFS does have distributed replicated feature which can
> replicate VM data in multiple bricks, but in GlusterFS you have to map the
> replicated bricks during creation and the data can only be replicated
> between the two (or multiple based on your replication numbers) bricks only.
>
> The advantage of this feature would be that you can add standalone
> nodes(odd/even numbers) in oVirt ecosystem and schedular can place VMs in
> such a balanced and optimized mode so that maximum number of VMs remain
> available after N nodes failure from M number of nodes(where M>N)
>
> Please put your valuable thoughts regarding the same.
>
> Request you to let me know if you need any further clarifications from my
> side.
>
> Thanks
>
> Kausik
>
>
>
>
>
> On Thu, Jun 26, 2014 at 6:23 PM, Gilad Chaplik <gchaplik at redhat.com>
> wrote:
>
>> Hi Kausik,
>>
>> If I understand correctly your question, we do support this flow.
>> In case of failure we migrate highly available VMs to other hosts, but
>> note that there could be a connectivity problem between engine an node, and
>> node can still communicate with the storage,
>> so to avoid that (split brain) you need to have PM configured for that
>> node, or manually confirm that the host has rebooted.
>>
>> We even added a feature lately (3.4's HA reservation [1]) that indicates
>> whether your HA VMs have enough resources in cluster in case of a node
>> failure.
>>
>> Thanks,
>> Gilad.
>>
>> [1] http://www.ovirt.org/Features/HA_VM_reservation
>>
>> ----- Original Message -----
>> > From: "kausik pal" <kausikpal.1 at gmail.com>
>> > To: users at ovirt.org
>> > Sent: Tuesday, June 24, 2014 8:06:10 PM
>> > Subject: [ovirt-users] Is this kind of VM replication possible using
>> oVirt    Schedular
>> >
>> > Hi All,
>> >
>> > PFA the two diagrams describing placement of the VMs during normal
>> condition
>> > and condition after two node failure in 5 node set up (Each Node can
>> host up
>> > to 6 VMs due to memory constraints).
>> >
>> > My question is whether this kind of VM replication as shown in the
>> attached
>> > diagram is possible utilizing oVirt schedular.
>> >
>> > The benefits of this kind of replication would be following :-
>> >
>> > 1. Any number of Hosts/Nodes can participate (Odd/Even) in the
>> > infrastructure.
>> >
>> > 2. We can add any number (odd/even) number of Nodes to re-balance the VM
>> > placement.
>> >
>> > 3. After node failures the Maximum number of VMs that can run on the
>> > remaining nodes can be calculated with the following formula:-
>> >
>> > Total No. of VMs running after node failure = ((Total No. of Nodes) -
>> (No. of
>> > failed Nodes)) * (Max. No. of VMs that can run per Node)
>> >
>> > The attached table gives a rough calculation on maximum number VMs that
>> can
>> > run after node failures.
>> >
>> >
>> > Please let me know if you need any further information from my side.
>> >
>> > Thanks
>> >
>> > Kausik
>> >
>> > _______________________________________________
>> > Users mailing list
>> > Users at ovirt.org
>> > http://lists.ovirt.org/mailman/listinfo/users
>> >
>>
>
>
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