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Re: [Xen-users] Cannot boot with LVM inside Xen DomU

On Sun, Jul 10, 2011 at 11:36 PM, Prakhar Srivastava
<prakhar.apj@xxxxxxxxx> wrote:
> Hi Oliver,
> Thanks a ton for all the valuable information.
> I am definitely not using the file based images. I am using LVM based root
> images for Xen guests using
>  disk = [ 'phy:/dev/Box1/debian-lvm-image,xvda,w' ]
> One very important point that I get from you is that doing rsync won't work
> for copying LVM based Dom0. So I am going to try dd command to copy the
> entire partition to a logical volume (/dev/Box1/debian-lvm-image).

What are you going to copy? dom0's PV? dom0's root LV?

> What still I am not getting is that what is issue with nested LVM
> configuration. Consider this ,
> /dev/Box1/debian-lvm-image will exist on Dom0 (node running the Xen
> hypervisor)
> /dev/Boc1/root will exist on DomU
> I can't visualize the existence of two volume groups in the system causing a
> conflict.

Not if the VG is created within domU.
It WILL cause a confflict if you try to create the VG from dom0, or
mount domU's LV on dom0.

>>The following is more likely:
> I checked the Dom0 grub configuration and observed that root is set to
> root=/dev/mapper/Box1-root
> This is the reason I was using root=/dev/mapper/Box1-root   (I am sorry I
> mentioned incorrect root=/dev/Box1/root in my last reply.)
> I will try to use root=/dev/xvda and keep the /etc/fstab intact.
> I  don't want to avoid installing Xen guest (what are the possible ways of
> installing a PV guest with LVM inside ? Should I try virt-install? ).

Reading your mail I got the impression that you don't fully understand
the concept of LVM (e.g. PV, VG, LV).
So at this point I highly suggest you use a GUI (e.g. virt-manager) to
setup the necessary config file, install domU from network install
(when using PV domU) or ISO image (when using HVM domU), and choose to
use LVM during domU install process. Forget everything you tried about
"root" or fstab (for now), and just let the installer do its thing.
When it's done, you can look at the resulting domU and config file to
have an idea on how a correct setup should look like.

In case you're wondering, yes, it IS possible to use LVM inside domU.
It's the default setup of used by RHEL/Centos. However the EASIEST way
to do so is by letting domU's installer run, and NOT by copying stuff
from dom0.

Hope that can get you started.


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