Re: [Xen-users] RHEL xen vs kvm

[Grant McWilliams <grantmasterflash@xxxxxxxxx>]

On Wed, Apr 21, 2010 at 7:26 PM, Jeff Sturm <jeff.sturm@xxxxxxxxxx> wrote:

 

In the end I don't know that we needed two hypervisors that are so similar, but we have them.  It's going to come down to something like choosing between Intel or AMD.  One might have a slight edge over the other at any moment, or be somehow more elegant than the other, but both are very capable and you can do a lot with them.

 

Jeff

 

At some point (and we're fast getting there) we'll be able to apply Linus' quote about the kernel not mattering to hypervisors. About now the hypervisor is starting to not matter and how you manage your VMs is the real reason to choose which system you use. 

Currently I only use Paravirtualization because it's about as fast as bare metal (databases are the worst for virtualization and mysqlbench shows performance within 1% of bare metal) and if you set them up with their own kernel inside the VM disk it looks and acts like a real Linux server. The other mode with Xen is HVM which is full virtualization and is necessary to virtualize Windows. KVM does a better job of this then Xen and is faster for full virt. However KVM isn't as fast as Xen PV even with KVM PV drivers. It all depends on what your needs are. If we go by the Xen summit slides the future of Xen is in hybrid virtualization which uses hardware virtualization for everything the hardware supports and then uses paravirtualization for everything else. This will be the best of both worlds (HVM and PV). I don't see KVM moving away from what it's doing (using Qemu for a lot of stuff, Hardware VT and paravirtualized network and disk drivers). How much of a difference this will make I'm not sure. 

Here's my thoughts.

If I were primarily virtualizing Windows I'd use KVM.
If I were primarily virtualizing Linux I'd use Xen.
If I was using a bunch of old 3.4 Ghz Dual Core Xeons (I am) I'd use Xen.
If I was wanting to nest VMs I'd use AMD CPUs and KVM (for now).
If I wanted the most pain free path to keeping my hypervisor updated I'd use KVM.
If I was doing desktop virtualization (local login, not network logins) I'd use KVM or VirtualBox
If I wanted the most tried and true enterprise hypervisor out there and didn't want to use VMWARE then I'd use Xen. Citrix Xenserver, VirtualIron, Sun SVM (one flavor), Oracle Virtual Machine and Amazon EC2 are all based on Xen.

It might look like I lean toward KVM from this list but I still prefer Xen in most cases because of category 2.

Grant McWilliams

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