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Re: [virt-tools-list] KVM Live Migration

----- Original Message -----
> From: "Mike Hall" <MHall astc nt gov au>
> To: virt-tools-list redhat com
> Sent: Wednesday, October 6, 2010 8:06:42 PM
> Subject: Re: [virt-tools-list] KVM Live Migration
> > Are the hosts "compatible" ?
> > eg. what hardware are they running - are there issue with
> > compatibility between then CPUs -eg. does host A have a newer cpu
> > (with newer features) than host b ?
> The machines are only compatible to the extent that both their CPUs
> support vtx. When we go into production both machines will be
> identical.
> One is a Dell PowerEdge 840 with Intel Xeon Quad Core (X3220 @
> 2.4GHz).
> The other is a HP Compaq dc7800p with Intel Core2 vPro (E8400 @
> 3.0GHz).

This could be the problem, after migration CPU features suddenly disappear.
Is the NX (no execute) flag set in the bios on both machines (or look for nx in flags section of /proc/cpuinfo).
Ideally you want to have identical machines for live migration, but there are ways in kvm to filter out CPU flags to assure compatibility.
Good article on this here http://berrange.com/posts/2010/02/15/guest-cpu-model-configuration-in-libvirt-with-qemukvm/

> The guests are all using only one vCPU.
> I have solved the lost-networking-on-migration issue - there was no
> bridge forwarding in iptables on second VM host.
> The reboot-on-migration issue remains however, and occurs both with
> CentOS 5.5 and Win7 guests. This is not a total show-stopper for us as
> in our environment we can afford to shut machines down and restart on
> another host, but live migration would be a nice feature.
> Side Note: Since the majority of those answering my questions on this
> list and the libvirt-users list are RedHat staff, thought I would
> point out that while we're testing on CentOS, we have actually
> purchased 5 RedHat subscriptions which are yet to be activated.

Thanks for that - we want to support the community but it's always nice to pay our engineers!


> Thanks again
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> virt-tools-list redhat com
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