[Discuss] choice of hypervisor

[tmetro+blu at gmail.com (Tom Metro)]

Richard Pieri wrote:
> KVM isn't a bare metal hypervisor like Xen. Every KVM guest is
> a process running on the Linux host. That's fine as a substitute for
> VMware Workstation but it's not so good for enterprise class virtual
> server racks.

What advantage do you see to a bare metal hypervisor?

A bare metal hypervisor may not be layered on top of a kernel, but it is
still acting as a kernel and doing most of the things a kernel does.

Presumably a bare metal hypervisor will be a bit more performance
optimized to run VMs. What do the benchmarks show for comparison?

I imagine a bare metal hypervisor has far narrower hardware support than
the Linux kernel. I'm also guessing the Xen bare metal hypervisor
borrows a lot from the Linux kernel.

If the best case you can make for using a bare metal hypervisor is that
 it prevents the system administrator from being tempted to run other
processes on the host, then that doesn't sound so compelling.


> It's also not so good for workstation virtualization since
> you can only run KVM guests on Linux hosts thus negating the easy
> portability that makes workstation virtualization so useful.	

So? Doesn't that same comment apply to Xen.

Are you trying to say KVM is useless because it is no good at the things
Xen is good at and it's no good at the things VirtualBox is good at?


> ...Amazon EC2 or Rackspace or Linode. They're only some of the largest VPS
> platforms in the world and they all run on Xen.

Linus wasn't the only one to turn up his nose at the ugliness of Xen's
internals. I'm a bit surprised that these large players have stuck with
Xen wile other technologies have caught up to its capabilities.

Why do you think that is? Inertia?

Why Rackspace Uses Xen for OpenStack
http://www.serverwatch.com/server-news/why-rackspace-uses-xen-for-openstack-video.html

  The original decision by Rackspace to use Xen was made around 2008. At
  that time, Xen was seen as being more stable than KVM. Additionally,
  Citrix has a relationship with Microsoft, which meant that Rackspace
  could get a higher level of Windows support.
  [...]
  OpenStack, which was initially created by Rackspace along with NASA,
  can run any number of hypervisors, although the open source KVM
  hypervisor might well enjoy a technological advantage.

  "Our decision to use Xen in OpenStack was largely due to the fact that
  we already had several thousand nodes deployed in Xen in another
  OpenStack environment and we wanted to make the transition
  easy," Toman said. "We also have a lot of operational knowledge
  managing large scale deployments of Xen hypervisors."

Apparently yes, inertia.

 -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/