A late reply, but hopefully a useful set of feedback for the archives:
On 04/20/2012 05:59 AM, Rafał Radecki wrote:
Key factors from my opint of view are:
- stability (which one runs more smoothly on CentOS?)
I found that xenconsoled could frequently crash in Xen dom0, and that guests would be unable to reboot until it was fixed. I also found that paravirt CentOS domUs would not boot if they were updated before the dom0. In short, Xen paravirt was very fragile and troublesome. I never tested Xen with hardware virtualization.
I have had no such problems with KVM. In my experience KVM is much more stable than Xen paravirtualization. Xen HVM probably would suffer at least some of the same problems.
- performance (XEN PV/HVM(with or without pv drivers) vs KVM HVM(with or
without pv drivers))
PV drivers will make some difference, but the biggest performance difference you'll see is probably the difference between file-backed VMs and LVM-backed VMs. File-backed VMs are extremely slow. Whichever system you choose, use LVMs as the backing for your guests.
- security
There have been bugs that allow guests to escalate privileges and access host resources, but they're relatively few. I don't think there's a significant difference between the two in this area.
Overall I advise the use of KVM. It should be more stable, and has the advantage of Red Hat support.