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Mainly I'm thinking of expandability - passing through your NICs to your domU directly means that each NIC can only be connected to one domU - and ease of configuration - passing through NICs means messing around with PCI settings, matching the right PCI bus identifier to the right NIC port, etc.
If you're testing performance of passthrough vs. bridge, I can see why you'd want to do that. I've got three servers set up to run a bunch of domUs (I have probably 30 running on 3 physical servers right now) and I need VLAN support plus network aggregation. All of this is easier to do in the dom0 and create a bunch of bridges that the domUs can connect to. Very similar to the way VMware's ESX does things. My servers are also 1U servers, so I don't have a lot of room to expand PCIe cards or anything like that - I have to make the most of the small amount of space given.
-Nick
>>> On 2008/04/24 at 16:54, Asim <linkasim@xxxxxxxxx> wrote:
Thanks Nick for all the information. Yes I want to do some performance
measurements
on pass-through I/O (and bridge I/O). So I just want one DomU. I guess
thats two NICs
one for each Dom*. Apart from lack of migration support, what are the
other disadvantages?
Also, how do i do this? Do i need to hide the PCI from Dom0 and add it
using network-attach script?
-Asim
On Thu, Apr 24, 2008 at 3:50 PM, Nick Couchman <Nick.Couchman@xxxxxxxxx> wrote:
>
>
> What is your reason for wanting to do passthrough I/O? The only really good
> reason I can think of for it is that you have an application that requires
> very high throughput and extremely low latency. Otherwise the bridge should
> be fine, and I can think of several reasons why you don't want to use
> passthrough I/O. One of which is the one you mentioned - migration will be
> worthless because your domUs will be hardware dependent.
>
>
> So, if you're still insistent upon doing passthrough I/O, then, yes, you'll
> need one network card for every domU you have running.
>
>
> -Nick
>
>
>
> >>> On Thu, Apr 24, 2008 at 2:39 PM, Asim <linkasim@xxxxxxxxx> wrote:
>
>
>
>
>
>
> > 2) You don't want to do direct NIC access to a domU, you want to use a
> > bridge. By default XEN creates a bridge (can't remember what they're
> > calling it these days) that bridges eth0 to all of your domUs. This
> should
> > allow you to use your single network card with as many domUs as you have
> on
> > your system.
> >
> >
>
> I want to do passthrough I/O for my specific needs and not use virbr0.
> I believe
> this will also disable migration if am not wrong? So, to do a direct NIC
> access
> I think I should hide this PCI from Domain-0, so will need a second
> additional
> NIC?
>
> -Asim
>
>
>
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