Re: [Xen-users] Re: upgrade leny-squeeze, xen3.2-xen4.0, what's wrong?

[Henrik Langos <hlangos-xen@xxxxxxxxxxxxxx>]

On Fri, Feb 11, 2011 at 10:04:44AM +0000, Mauro wrote:
> On 11 February 2011 08:59, Henrik Langos <hlangos-xen@xxxxxxxxxxxxxx> wrote:
> > Hi Mauro,
> >
> > It would be more useful if you had included the /etc/xen/mail1.cfg
> > as that is the file ultimately used to create the domU. The xen-tools.conf
> > is just a tool that does a some (actually quite good) work for you by
> > creating that file and the disk/partition volumes. xen-tools is not involved
> > in *running* those VMs though.
> >
...
> >
> > My (wild) guess on this would be that you'd have to change the "root=" 
> > parameter
> > in your config file to point to some "sda*" device/partition instead of 
> > "xvda*".
> >
> > root = "/dev/xvda2"
> > to
> > root= "/dev/sda2"
> >
> >
> > Alternatively you'd have to change the "disk=" parameters to map your LVs 
> > to xdva*
> > instead of sda*.
> >
> > disk        = [
> >                  'phy:/dev/vg00/mail1-swap,sda1,w',
> >                  'phy:/dev/vg00/mail1-disk,sda2,w',
> >              ]
> > to
> > disk        = [
> >                  'phy:/dev/vg00/mail1-swap,xvda1,w',
> >                  'phy:/dev/vg00/mail1-disk,xvda2,w',
> >              ]
> >
> >
> >> I've solved using pygrub.
> >> So it seems that without pygrub I can't run DomUs?
> >
> > You shouldn't have to use pygrub for something that simple.
> >
> > My guess is that there was a lack of communication between the
> > maintainers of xen and xen-tools in regard to the default devices.
> >
> 
> mail1.cfg:
> 
> bootloader = '/usr/lib/xen-default/bin/pygrub'
> 
> vcpus       = '4'
> memory      = '2048'
> 
> #
> #  Disk device(s).
> #
> root        = '/dev/xvda2 ro'
> disk        = [
>                   'phy:/dev/vg00/mail1-disk,xvda2,w',
>                   'phy:/dev/vg00/mail1-swap,xvda1,w',
>               ]
> 
> 
> #
> #  Physical volumes
> #
> 
> 
> #
> #  Hostname
> #
> name        = 'mail1'
> 
> #
> #  Networking
> #
> vif         = [ 'ip=172.16.10.154,mac=00:16:3E:01:D7:24' ]
> 
> #
> #  Behaviour
> #
> on_poweroff = 'destroy'
> on_reboot   = 'restart'
> on_crash    = 'restart
> 
> It's exactly as another DomU that runs with xen 3.2 on a debian lenny machine.
> The only difference is the bootloader = '/usr/lib/xen-default/bin/pygrub'.

Well,

There is no "kernel=" or "ramdisk=" parameter in your mail1.cfg.
So I guess you removed those when you switched to using pygrub?

If you want to know what really changed when switching from lenny to 
squeeze you could change it back to try the two fixes that I mentioned.

> I've noticed that when debootstrap install the system it install the
> linux-image and not linux-modules.
> >From mail1.log, debian squeeze and xen4.0:
> 
> The following extra packages will be installed:
>   firmware-linux-free libuuid-perl linux-base linux-image-2.6.32-5-xen-amd64
> Suggested packages:
>   linux-doc-2.6.32 grub
> The following NEW packages will be installed:
>   firmware-linux-free libuuid-perl linux-base linux-image-2.6.32-5-xen-amd64
>   linux-image-xen-amd64
> 
> While from mail1.log with xen3.2 and debian lenny:
> 
> The following NEW packages will be installed:
>   linux-modules-2.6.26-2-xen-amd64
>

Wow, that, I think, is a good thing! The linux-image package contains the 
modules
but by also including the kernel and the base packages it will leave you with a 
much more "complete" domU.

You could not have booted the old lenny domU with pygrub because the domU file 
system
didn't even contain a kernel image or initrd. Those were always taken from 
dom0's /boot/.
Thats what the "root=" and "ramdisk=" parameters in your mail1.cfg are for. BUT 
that made
your domU depend much more on the state of your dom0.

Now with pygrub you can update the kernel in domU, have it reboot and pygrub 
will pick
up the new kernel from your domU's file system when xen creates your domU VM. 
(be sure 
to read and *understand* the release notes on xen/pygrub/grub2 issues though).

I personally like that change. It will make it easier to migrate PVM domUs that 
I create
with squeeze to the next debian release. Currently I have PVM domUs from Etch 
and Lenny 
on top of a squeeze xen-4.0.1 linux-2.6.32 and I had to copy the old domU 
kernels and 
initrds to my squeeze box as well as the /etc/xen/machine.cfg files and the 
domUs disk
images.

In the future I will only need the config file and the disk images. (Actually 
my domU's
disk images are now on an iSCSI storage now. So I will not have to worry about 
migrating
those and ultimately I want to move even the config files to a location that is 
shared
by all my xen dom0 hosts. But thats a different story and I guess I'll have to 
read up
on GFS(2?) or some other cluster file system.)

cheers
-henrik



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