[dundee] Virtual Question,

[Gordon Dunlop]

Arron Finnon wrote:
> Hiya All,
>
> Just a quick question for you all (and Gordon in particular); what's 
> the best Virtual Machine software?  I have used VMWare Server and i 
> have used VirtualBox as well, just kinda wanted to get everyone's 
> opinion on it.
>
> Arron
>
> _________________________________________________________________
I feel this will be a long post, I will try to keep it short. 
Virtualisation technology has come on in leaps and bounds during the 
past year as IT server infrastructures are realising the vast potential 
benefits. It can be like horses for courses as different virtualisation 
technologies meet different requirements.

_Para-Virtualisation_

Xen -  A modified Linux kernel that uses a hypervisor  that lies between 
the physical hardware and the operating system. Gives near to native 
performance with  slight performance loss when page tabling  and using 
system calls due to guest vm requiring extra hypercall permissions. Xen 
is favoured by large IT corporations for server consolidation and can 
have up to 32 operating systems running concurrently. Development is in 
progress to utilise Xen in the slave nodes of the OSCAR clustering 
system which would greatly enhance the potential of large clustering 
systems, at the moment it can only be deployed in the head nodes. Best 
use for running multiple server functions.

User-Mode Linux - A full Linux kernel with VM and scheduler as the host. 
Forget this as it can run only one process per gust through the host 
scheduler. Xen beats the pants off UML for performance.

_Paene-Virtualisation

_OpenVZ  - Commercial version called Virtuozzo, which Abertay is going 
to deploy (ask Jason). Creates Virtual Private Servers (100's) where the 
virtual servers run on top of the operating system using namespace 
isolation. This has the best performance  as it does not require a 
hypervisor reducing  system calls.  I have found it can even beat native 
performance due to the developers getting rid of coding errors from the 
native kernel and  providing better coding paths. Best use for running 
multiple users like within a University setup.

_Full Virtualisation_

VMware - Where modification of host operating system is not required and 
where all hardware resources and machine-privileged instructions are 
virtualised. There is normally a large overhead with full virtualisation 
but has been greatly reduced. VMware is talking about going 
para-virtualised in the  future so this is the one to watch. This  
method is preferred by large IT structures that operate heterogenous 
operating system environments. I have been impressed with  VMware Server.

Virtualbox - I have not used this yet, so Arron can let me know what he 
thinks. I was reading that there is a less of a problem with USB devices 
with VirtualBox than with VMware Server. I might try VirtualBox next month.

_General


_Xen and OpenVZ code are being added, bit by bit, to the Linux kernel 
with the aim of having  Xen and OpenVZ fully merged in the Linux kernel. 
That is the aim ,but there are some minor disputes going on.The Linux 
kernel now has base paravirtualisation and a Kernel-based Virtual 
Machine (KVM) (needs Intel and AMD processors that has vitualisation 
technology in their instruction sets for running Windows XP in Linux), a 
full virtualisation solution, incorporated into its architecture. IBM 
and Xen are collaborating to produce a neutral interface that will lie 
between the Linux kernel and the virtualisation hypervisor that will 
allow the operation of different types of virtualisation. The aim here 
is for an organisation or individual that can pick and choose the type 
of virtualisation required using just one Linux distribution.
 
I think I've kept it reasonably short,

Gordon