[ovirt-users] oVIRT 4.1 / iSCSI Multipathing

[Nicolas Ecarnot]

Hello,

[Unusual setup]
Last week, I eventually managed to make a 4.2.1.7 oVirt work with 
iscsi-multipathing on both hosts and guest, connected to a Dell 
Equallogic SAN which is providing one single virtual ip - my hosts have 
two dedicated NICS for iscsi, but on the same VLAN. Torture-tests showed 
good resilience.

[Classical setup]
But this year, we plan to create at least two additional DCs but to 
connect their hosts to a "classical" SAN, ie which provides TWO IPs on 
segregated VLANs (not routed), and we'd like to use the same 
iscsi-multipathing feature.

The discussion below could lead to think that oVirt needs the two iscsi 
VLANs to be routed, allowing the hosts in one VLAN to access to 
resources in the other.
As Vinicius explained, this is not a best practice to say the least.

Searching through the mailing list archive, I found no answer to 
Vinicius' question.

May a Redhat storage and/or network expert enlighten us on these points?

Regards,

-- 
Nicolas Ecarnot

Le 21/07/2017 à 20:56, Vinícius Ferrão a écrit :
>
>> On 21 Jul 2017, at 15:12, Yaniv Kaul <ykaul at redhat.com 
>> <mailto:ykaul at redhat.com>> wrote:
>>
>>
>>
>> On Wed, Jul 19, 2017 at 9:13 PM, Vinícius Ferrão <ferrao at if.ufrj.br 
>> <mailto:ferrao at if.ufrj.br>> wrote:
>>
>>     Hello,
>>
>>     I’ve skipped this message entirely yesterday. So this is per
>>     design? Because the best practices of iSCSI MPIO, as far as I
>>     know, recommends two completely separate paths. If this can’t be
>>     achieved with oVirt what’s the point of running MPIO?
>>
>>
>> With regular storage it is quite easy to achieve using 'iSCSI bonding'.
>> I think the Dell storage is a bit different and requires some more 
>> investigation - or experience with it.
>>  Y.
>
> Yaniv, thank you for answering this. I’m really hoping that a solution 
> would be found.
>
> Actually I’m not running anything from DELL. My storage system is 
> FreeNAS which is pretty standard and, as far as I know, iSCSI 
> practices dictates segregate networks for proper working.
>
> All other major virtualization products supports iSCSI this way: 
> vSphere, XenServer and Hyper-V. So I was really surprised that oVirt 
> (and even RHV, I requested a trial yesterday) does not implement ISCSI 
> with the well know best practices.
>
> There’s a picture of the architecture that I take from Google when 
> searching for ”mpio best practives”: 
> https://image.slidesharecdn.com/2010-12-06-midwest-reg-vmug-101206110506-phpapp01/95/nextgeneration-best-practices-for-vmware-and-storage-15-728.jpg?cb=1296301640
>
> Ans as you can see it’s segregated networks on a machine reaching the 
> same target.
>
> In my case, my datacenter has five Hypervisor Machines, with two NICs 
> dedicated for iSCSI. Both NICs connect to different converged ethernet 
> switches and the iStorage is connected the same way.
>
> So it really does not make sense that a the first NIC can reach the 
> second NIC target. In a case of a switch failure the cluster will go 
> down anyway, so what’s the point of running MPIO? Right?
>
> Thanks once again,
> V.
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