XenServer Converting HVM to Parravirtualised

Hi everyone,

Recently I have been tasked with the daunting process of converting a setup of HVM enabled VMs (running on Citrix XenServer 5.6.0) into PV (paravirtualised) containers.

The constraints of the project was that:

1) The operating system must be functionally identical after the migration. 2) minimal modification to the operating system (with exception of kernel / drive mapping)

I also was allowed to change the bootloader(ie, grub) in what ever way I see fit.

However, I have attempted this, I will firstly like to show you my steps I took.

This at the moment is CentOS5.5 specific:

---Steps:

1) yum install kernel-xen

This installed: 2.6.18-194.32.1.el5xen

2) edited: /boot/grub/menu.lst changed my specs to match:

title CentOS (2.6.18-194.32.1.el5xen)

root (hd0,0)

kernel /vmlinuz-2.6.18-194.32.1.el5xen ro root=/dev/VolGroup00/LogVol00 console=xvc0

initrd /initrd-2.6.18-194.32.1.el5xen.img

Then I changed my xenserver parameters to match:

xe vm-param-set uuid=[vm uuid] PV-bootloader-args="--kernel /vmlinuz-2.6.18-194.32.1.el5xen --ramdisk /initrd-2.6.18-194.32.1.el5xen.img"

xe vm-param-set uuid=[vm uuid] HVM-boot-policy=""

xe vm-param-set uuid=[vm uuid] PV-bootloader=pygrub

xe vbd-param-set uuid==[Virtual Block Device/VBD uuid] bootable=true

Some things to note, I am running a VolGroup LVM ;)

Anyways, after all these steps (which aren't much!) I boot the VM and it boots initial kernel just fine, however I am presented with this error:

-----------------BOOT SCREEN-------------------
device-mapper: dm-raid45: initialized v0.2594l

Waiting for driver initialization.

Scanning and configuring dmraid supported devices

Scanning logical volumes

Reading all physical volumes. This may take a while...

Activating logical volumes

Volume group "VolGroup00" not found

Creating root device.

Mounting root filesystem.

mount: could not find filesystem '/dev/root'

Setting up other filesystems.

Setting up new root fs

setuproot: moving /dev failed: No such file or directory

no fstab.sys, mounting internal defaults

setuproot: error mounting /proc: No such file or directory

setuproot: error mounting /sys: No such file or directory

Switching to new root and running init.

unmounting old /dev

unmounting old /proc

unmounting old /sys

switchroot: mount failed: No such file or directory

-----------/ENDBOOT-----------------

Now my hints are that it cannot detect / because of the fact that when you change from HVM mode to PV it does something (not that obvious)

When you make a SR (storage) on a HVM, you get it mounted to the guest os as /dev/hda.

However in PV mode, this presents itself as /dev/xvda...

Could this be the answer? and if so, how the heck to I implement it??

I am truly stumped at this point :)

--Karl.