On Thu, 27 Mar 2008 11:30:04 +0000, Andy Smith <andy@???> wrote:
> Ubuntu's Xen kernels are really poor. They are full of bugs and
> crash continuously. I have found them unusable for domU in
> production so I dread to think what dom0 is like. Maybe HVM is
> better though.
I've not had particular problems with them. We run Ubuntu 6.06 domUs and a
7.04 dom0 under PV for our web services and haven't had any crashes so far.
> HVM is going to be quite slow compared to PV because of the emulated
> block and net drivers.
Hmm, Hugo suggested the other way round. :/
>> The domUs both have 100Mbit cards, using the default Realtek chip.
> Having
>> read the Xen networking guide[1], as far as I can tell each domU is
> only
>> able to use 100Mbit on its NIC. Is it possible to get domUs to emulate
>> gigabit NICs, or otherwise increase the bandwidth available to a given
>> domU?
>
> I don't believe so - the driver you get is the driver you get. Can
> you run the Linux domain in PV mode?
I could try it, but I'm getting conflicting advise on performance. Apart
from the option of passing the card through, I'm not sure what the
difference could be under PV as the same NIC is emulated, AFAICT.
> I am not sure that there are any GPL PV drivers (for use in HVM) for
> Linux -- Citrix and others sell proprietary ones I think. I have
> skimmed through threads on xen-user that suggest James Harper has
> some Windows PV drivers for block and net under development and
> available for experimental use (GPL).
I'll keep an eye on that. Unless I've misunderstood, surely the problem is
as much which NICs the hypervisor knows how to present to the domUs as the
drivers for the OS inside the domU itself?
> Have you tried KVM at all?
I have, but it didn't play nicely at all with our hardware. The main reason
for trying it was to do p2v stuff which then spectacularly failed. Given
that we are already running Xen it made sense to stick with the technology
we've got experience with.
> BTW even with paravirtual net drivers I do not think you will see
> much beyond 100Mbit/s per stream -- the most I've managed between PV
> domains on two different hosts on the same gigabit LAN is about
> 130Mbit/s. Will probably still help for multiple streams though.
I suspect I'm going to end up finding a way of hooking up the second NIC
and passing it through to the domU I want to give more bandwidth.
Thanks,
Tony
