Enabling Virtual Machine support

[Tom Buskey]

On Mon, Sep 28, 2009 at 8:17 AM, Jerry Feldman <gaf at blu.org> wrote:

>
> 1. Most systems disable the VT extensions in the BIOS by default (AMD
> and Intel)> I have an AMD quad core Opteron with VMX, with a Tyan mother
> board. The VMX bit shoed up in the processor flags (/proc/cpuinfo), but
> I found it was disabled in the BIOS until I manually turned it on.
>
>
I've always been annoyed by that.  By default hyperthreading is usually
turned off as well.  I know of a few cases where hyperthreading caused
problems.  I haven't heard of anything where the VT-x/AMD's hardware
Virtualization support causes problems.  Ben brings up a good point about a
possible security risk, but motherboard manufactures haven't worried about
it much in the past.



> 2. Under Linux your choices for VMMs (Virtual Machine Managers) are
> basically KVM/QEMU, QEMU(software), Xen, Virtualbox, and VMWare. Xen and
> KVM do use the virtualization hardware.  So far, I don't see any need
> for virtualization hardware for Virtualbox or the free versions of
> VMWare. If you are using virtualization on a server, more homework is
>

I've found the hardware support speeds up VMware Server and VirtualBox quite
a bit.  It's definitely worth spending more on the system for.  Of course,
most recent CPUs have it built in.

I think there's also something about the hardware virtualization that
enables non XEN kernels (Windows) to run on a XEN server but I'm not sure on
that point.

There might be something about KVM that requires the hardware too.


> needed because, in general, performance is more critical. I'm not sure
> if Virtualbox supports 64-bit guests, but KVM/QEMU and VMWare certainly
> do. Both KVM, QEMU, and Virtualbox are released via the GPL license. I'm
>

VirtualBox will support a 64 bit guest with 1 or more CPUs on a 32 bit
single CPU host.  It will also do OpenGL amd DirectX.  It gets updated every
month or so with capabilities.


> not sure about Xen since Citrix bought it, but you need a Xen-enabled
> kernel to run Xen. The KVM modules are bundled with all the recent 2.6
> kernels. The Virtualbox modules generally keep up, but I have had a
> kernel update where the VBox module was not updated, but that usually
> required a quick yum or apt update.
>

Of all the hypervisors, I feel VirtualBox is the easiest to maintain.  I've
done VMware Server, ESXi and played with KVM.  I wonder about the
performance differences but not enough to test :-)
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