[openstack-dev] [nova]Why not allow to create a vm directly with two VIF in the same network

Vishvananda Ishaya vishvananda at gmail.com
Wed Jan 29 04:19:52 UTC 2014

On Jan 24, 2014, at 6:33 AM, CARVER, PAUL <pc2929 at att.com> wrote:

> I agree that I’d like to see a set of use cases for this. This is the second time in as many days that I’ve heard about a desire to have such a thing but I still don’t think I understand any use cases adequately.
> In the physical world it makes perfect sense, LACP, MLT, Etherchannel/Portchannel, etc. In the virtual world I need to see a detailed description of one or more use cases.
> Shihanzhang, why don’t you start up an Etherpad or something and start putting together a list of one or more practical use cases in which the same VM would benefit from multiple virtual connections to the same network. If it really makes sense we ought to be able to clearly describe it.

I can think of one potential use case. In testing I have been unable to saturate a 10g link using a single VM. Even with multiple streams, the best I have been able to do (using virtio and vhost_net is about 7.8g. I have been told with CPU pinning that can be pushed up into the high nines, but pinning is not a great fit for cloud. I am not totally sure where the bottleneck is, but I have a guess that it relates to maxing out a single cpu on the host side pushing traffic from the virtual interface into the physical one. I have been able to saturate a 10g link by using multiple vms, but it occurs to me that having two separate vnics might allow you to push the full 10g from a single vm. I have not tested this, but I wouldn’t be surprised if it is true.


> --
> Paul Carver
> VO: 732-545-7377
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> E: pcarver at att.com
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> From: Day, Phil [mailto:philip.day at hp.com] 
> Sent: Friday, January 24, 2014 09:11
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [nova]Why not allow to create a vm directly with two VIF in the same network
> I agree its oddly inconsistent (you’ll get used to that over time ;-)  - but to me it feels more like the validation is missing on the attach that that the create should allow two VIFs on the same network.   Since these are both virtualised (i.e share the same bandwidth, don’t provide any additional resilience, etc) I’m curious about why you’d want two VIFs in this configuration ?
> From: shihanzhang [mailto:ayshihanzhang at 126.com] 
> Sent: 24 January 2014 03:22
> To: openstack-dev at lists.openstack.org
> Subject: [openstack-dev] [nova]Why not allow to create a vm directly with two VIF in the same network
> I am a beginer of nova, there is a problem which has confused me, in the latest version, it not allowed to create a vm directly with two VIF in the same network, but allowed to add a VIF that it network is same with a existed VIF'network, there is the use case that a vm with two VIF in the same network, but why not allow to create the vm directly with two VIF in the same network?
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