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Re: [fedora-virt] P2V and grub bootloader



On 04/30/2009 11:39 PM, Richard W.M. Jones wrote:
On Thu, Apr 30, 2009 at 11:28:51PM +0200, Dennis J. wrote:
Hi,
I'm currently experimenting with converting a physical system to a
virtual one. Using losetup, kpartx, etc. i was able to transfer the
system to a volume group in an image file.

Why not just copy across the whole block device?  This is essentially
what virt-p2v does (http://et.redhat.com/~rjones/virt-p2v/), although
virt-p2v is doing nothing more than automating what you could do by
hand.

Anyway, if you copy the whole block device (eg /dev/sda) then
presumably grub will be copied across along with it.

virt-p2v's achilles heel for me is that it can only copy on the block device level. /dev/sda is 50gb in size, the root logical volume only 10gb and copying the files over by piping a tar into ssh allowed me to shrink it to 5gb in the process. also I plan to move machines that use regular partitioning into VMs that use LVM volumes. Also copying the 3gb of files is obviously faster then copying 50gb of mostly empty space.

How can I install grub from outside the VM?

I haven't tried it, but it's possibly something you can do from
libguestfs, or if not, it's something that we could add to libguestfs.

That would be great. What I'm a little confused about is the different perspectives of the device-space you get when simply chroot-ing into the VMs root filesystem and actually booting the VM. In the VM booting case /dev/sda is /dev/sda so a "grub-install /dev/sda" does the trick but in the chrooting case /dev/sda is still the physical /dev/sda (if I'm not making a mistake in my thinking here). That's why I thought I could "grub-install /dev/loop0" to treat the image file as the virtual /dev/sda. Unfortunately that seems to confuse grub. I think I'll have to dive into the grub-install source to see why exactly it is complaining and how to get around that.

Regards,
  Dennis


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