Is it possible to live migrate guest OS'es between different versions of kvm/qemu-kvm?

Hi,

I currently have a couple of Debian KVM servers with all a different version of kvm or qemu-kvm.

I can live migrate a guest OS from one server to the other just fine, as long as the version of qemu-kvm is the same. (Thanks to Gleb Natapov who helped me solve my ARP announce problem yesterday)

However, when I try to migrate a guest to a server running a newer (or older) version of qemu-kvm, I run into problems. I think this is because the xml configuration differs slightly between version.

For example, if I try to migrate from a server running qemu-kvm 0.11.0 to one running qemu-kvm 0.12.4, I get the following error:

virt01:~# virsh migrate --live testserver qemu+ssh://192.168.1.7/system
error: internal error unable to reserve PCI address 0:0:3

When migrating from kvm 85 to qemu-kvm 0.11.0:

virt02:~# virsh migrate --live testserver qemu+ssh://192.168.1.2/system
error: Unknown failure

Migrating one from 0.12.4 to 0.11.0 just completely breaks libvirt, forcing me to kill -9 libvirtd and the kvm instance, etc.

I believe this is caused in part because different versions of qemu-kvm need different xml configurations. To run my testserver on 0.12.4 for example, I need to delete the lines with the PCI id's, just to be able to start the it.

So, is there a way to make this work? Perhaps without libvirt? Or tell libvirt to not send the config file when doing a live migrate, and use the xml in /etc/libvirt/qemu instead somehow?

Thanks in advance,

Nils

Hey guys,

next try is without libvirt, but still no joy.

After issuing 'migrate -d <url>' on my sending host (qemu-kvm 0.11.0), I get the following output on the receiving host (qemu-kvm 0.12.4):

(qemu) Unknown savevm section or instance 'slirp' 0 load of migration failed

... leaving my vm broken.

Am I doing something wrong, or is the format of the savevm file just different and should I abandon all hope of ever doing a live migration to a newer version of qemu-kvm?

Thanks in advance,

Nils

---

Here are my upstart options on the 'sender':

/usr/bin/kvm -S \
        -M pc-0.11 \
        -enable-kvm \
        -m 512 \
        -smp 2,sockets=2,cores=1,threads=1 \
        -name testserver \
        -uuid 890a0156-0542-32d8-66d7-b36a711084cc \
        -monitor 
unix:/var/lib/libvirt/qemu/testserver.monitor,server,nowait \
        -boot c \
        -drive 
file=/dev/disk/by-path/ip-192.168.3.100:3260-iscsi-iqn.2003-10.com.lefthandnetworks:lefthand0:64:testserver-lun-0,if=virtio,boot=on \
        -drive media=cdrom \
        -usb \
        -vnc 0.0.0.0:10 \
        -k en-us \
        -vga cirrus &

And the 'receiver':

/usr/bin/kvm -S \
        -M pc-0.11 \
        -enable-kvm \
        -m 512 \
        -smp 2,sockets=2,cores=1,threads=1 \
        -name testserver \
        -uuid 890a0156-0542-32d8-66d7-b36a711084cc \
        -nodefaults \
        -chardev 
socket,id=monitor,path=/var/lib/libvirt/qemu/testserver.monitor,server,nowait \
        -mon chardev=monitor,mode=readline \
        -boot c \
        -drive 
file=/dev/disk/by-path/ip-192.168.3.100:3260-iscsi-iqn.2003-10.com.lefthandnetworks:lefthand0:64:testserver-lun-0,if=none,id=drive-virtio-disk0,boot=on \
        -drive if=none,media=cdrom,id=drive-ide0-1-0 \
        -device 
ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 \
        -device 
virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 \
        -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 \
        -chardev pty,id=serial0 \
        -device isa-serial,chardev=serial0 \
        -usb \
        -vnc 0.0.0.0:0 \
        -k en-us \
        -vga cirrus \
        -incoming tcp:0:4444 &

A quick search of this and/or the qemu mailing lists would have told you this is unsupported.

It should work between 0.12 and 0.13, though.

error compiling committee.c: too many arguments to function

Is this something we can depend on for future releases then?

If we decide now to build a virtual hosting farm on 0.12, will we be able to use live migration in the future if we decide we want to upgrade to 0.13 or later?

N.

On 09/03/2010 02:35 PM, Nils Cant wrote:

First, don't trim the cc list. It's evil.

I believe so. Juan, can you confirm?

error compiling committee.c: too many arguments to function

Hey Juan,

do you also think future releases of kvm will have support for live migration from older versions? We're quite keen on knowing this, as we need to make a decision on what to build our stuff on. Being able to transparently move virtual servers onto a host running a newer version is definitely a feature we need...

Thanks in advance,

Nils