Mailinglist Archive: opensuse-virtual (37 mails)

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Re: [opensuse-virtual] Problems with Xen-installation resp.configuration
  • From: "Jason Douglas" <jdouglas@xxxxxxxxxx>
  • Date: Mon, 19 May 2008 13:11:25 -0600
  • Message-id: <48317C7D.971B.006F.0@xxxxxxxxxx>
On Sun, May 18, 2008 at 10:32 AM, in message <20080518163240.56670@xxxxxxx>,
<gildo.rex@xxxxxx> wrote:
I have got one more challenge to master:

As I'm doing clustertest I'm installing the VMs on one host and test them on
this host. The

next step is to spread the VMs across to hosts. So I need to migrate on of
the DomUs.
With VMware I simply copied the VM to the other physical node and started
I tried the same with the DomU and copied the configfile as well as the

When I try to start the DomU on the other node, I get the error message:

mpiphysicaltest2:~ # /usr/sbin/xm create /etc/xen/vm/test2 -c
Using config file "/etc/xen/vm/test2".
Error: (2, 'Invalid kernel', 'xc_dom_compat_check: guest type xen-3.0-x86_32
not supported

by xen kernel, sorry\n')

I checked the kernel via 'uname':

stephan@mpiphysicaltest1:~> uname -a
Linux mpiphysicaltest1 #1 SMP 2008/02/10 20:01:04 UTC i686
i686 i386 GNU/Linux
stephan@mpiphysicaltest1:~> uname -r

stephan@mpiphysicaltest2:/usr/lib/xen/boot> uname -a
Linux mpiphysicaltest2 #1 SMP 2008/02/10 20:01:04 UTC
i686 i686 i386 GNU/Linux
stephan@mpiphysicaltest2:/usr/lib/xen/boot> uname -r

On the second node (target node), the kernel seems to have a PAE-extension.
Might that hinder the migration? I don't know where it derives from - I
installed both kernel from the same CD from scratch...

There are two different 32-bit xen kernels shipped with openSUSE 10.3:
kernel-xen and kernel-xenpae. (Note that there are different hypervisor
versions that match these kernel versions as well [xen.gz and xen-pae.gz]).
These kernels mirror the kernel-smp and kernel-bigsmp that are typical in SuSE
distributions, and they are installed automatically based on the amount of
memory in your system (basically <= 2GB installs the kernel-xen; > 2G installs
the kernel-xenpae). The kernel within the guest* has to match the flavor of
the kernel that is running on the host (i.e. if you are running -xenpae, your
guest must be running -xenpae).

NOTE: I am only speaking of paravirtualized guests in this case. The kernel in
a fully virtualized guest does not need to match the "flavor" of the
hypervisor/dom0 kernel with the exception that you have to be running a 64-bit
xen in order to run any 64-bit guest.

How can I harmonize this??

There are a couple of different approaches that you can take here. One option
is to make both hosts run the same flavor of xen. Since there are only a
handful of processors newer than the Pentium Pro that do not have PAE support,
my recommendation would be to install the kernel-xenpae package into your host
that is currently running the -xen kernel. This will automatically create a
new entry in your grub menu that will load the right hypervisor as well.

However, if you choose this route, you will want to install the kernel-xenpae
kernel into all of your guests BEFORE you move to the xenpae kernel on the
host. Otherwise, your VM won't boot on either system and you'll have to use
some tricks to install the correct kernel in the vm (read "Requires you to be
somewhat of a Linux expert"). You'll also need to change your config file to
point at the -xenpae kernel, but I'll explain that in a moment.

This leads me to the second option which is to install BOTH kernels in your VM.
That way, by changing a single line in your vm config file, you'll be able to
boot the VM on either machine without changing the hypervisor that is currently
running. The line that you'll need to change is the one that references
/boot/kernel-xen and /boot/initrd-xen (I believe it is the bootargs line, but
without looking at your config file, I can't be sure). Once you have installed
the kernel-xenpae package into the guest, you can copy it to the PAE host and
change those entries to -xenpae. If you have problems with this, attach your
vm config file and any error messages, and I'll take a look.

Have a lot of fun!


P.S. If you are interested in actual VM migration (movement of the VM while it
is still running), you'll need to have both hosts running the same flavor of
xen, and you'll need the VM disk to be accessible to both machines in the exact
same way (i.e. iscsi target, nfs mount, or other). But for now, this should be
plenty to get you started. Good luck!
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