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xen-users
Re: [Xen-users] RHEL xen vs kvm
On Wed, Apr 21, 2010 at 11:42:31PM -0700, Grant McWilliams wrote:
> On Wed, Apr 21, 2010 at 7:26 PM, Jeff Sturm <[1]jeff.sturm@xxxxxxxxxx>
> wrote:
>
> Â
>
> 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.
>
> Â
>
> Jeff
>
> Â
>
> 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.
>
Do you have some benchmarks to prove KVM being faster than Xen HVM?
> 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.
Why? Xen has both the GPLPV Windows drivers, and the binary WHQL Citrix Windows
PV drivers available today.
> 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).
>
Xen also now has patches to supported Nested virtualization on both Intel and
AMD.
I bet this will end up in the Xen 4.1 development tree in upcoming weeks.
> 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.
>
There are a lot of options for Xen dom0 kernel nowadays.. although extra
patching
or fetching the git tree is still needed.
http://wiki.xensource.com/xenwiki/XenDom0Kernels
-- Pasi
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