How to startup OL6 as PVM under Oracle VM 2.X

Jephe Wu -

Problem:  Oracle VM 2.2 cannot startup default OL 6.3 as PVM (Oracle Linux 6.3 VM is created from downloaded assembly .ova file), although it can startup as HVM.

Error message:
After xm create vm1.cfg, it immediately return error like this:

 Error: Boot loader didn't return any data

Reason:  Oracle VM 2.2 cannot read ext4 /boot partition to find kernel to boot up as PVM
Soluton:  bootup this OL 6.3 on Oracle VM 3 hypervisor,  then convert /boot to ext3, then copy system.img to Oracle VM 2 to use.

1. check image file 
[root@dr01 xen]# file vm1.img
vm1.img: x86 boot sector, GRand Unified Bootloader (0.94); partition 1: ID=0x83, active, starthead 0, startsector 2048, 208896 sectors; partition 2: ID=0x83, starthead 0, startsector 210944, 20760576 sectors; partition 3: ID=0x82, starthead 63, startsector 20971520, 4194304 sectors, code offset 0x48

[root@dr01 xen]# mount dr01.img -o offset=$((512*2048)) /tmp/a
mount: unknown filesystem type 'ext4'

note: /boot partition is ext4 which is not recongized by Oracle VM server 2.2

2. boot up image on OVM3.1.1 then convert /boot from ext4 to ext3

#boot up OL 6.3 64bit VM as PVM on Oracle VM server 3.1.1
cp /boot /boot2 -va
umount /boot
mkfs -t ext3 /dev/xvda1
vi /etc/fstab to change /boot partition type from ext4 to ext3
mount /boot
cp /boot2/* /boot/ -va

3. boot up new image with 'xm create vm1.cfg' as follows

[root@dr01 xen]# more vm1.cfg
vif = ['type=netfront,bridge=fe', 'type=netfront,bridge=stor']
OVM_simple_name = 'vm1'
disk = ['file:/xen/vm1.img,xvda,w']
uuid = '0004fb00-0006-0010-07aa-15a5c3b8c419'
on_reboot = 'restart'
cpu_weight = 27500
memory = 4096
cpu_cap = 0
maxvcpus = 4
OVM_high_availability = False
maxmem = 4096
OVM_description = ''
on_poweroff = 'destroy'
on_crash = 'restart'
bootloader = '/usr/bin/pygrub'
name = 'vm1'
guest_os_type = 'default'
vfb = ['type=vnc,vncunused=1,vnclisten=,keymap=en-us']
vcpus = 4
OVM_os_type = 'None'
OVM_cpu_compat_group = ''
OVM_domain_type = 'xen_pvm'

4. file system corrupted for / sometimes during reboot and give error message like
xvda: barrier or flush: disabled

Please refer to 
Ubuntu 12.04 on Xen: blkfront: barrier: empty write xvda op failed
Solution: to add barrier=0 to mount options for all your local file system.