[opensource] Virtualization Technologies (Xen)

[Jim Dinan]

Srini wrote:
> Does anybody have any links or documentation for installing Xen on an 
> existing CentOS server so I can install other CentOS servers on top of 
> it for separating Webserver with DNS?
> Also, is it advisable to use Xen or should I use VMWare if I intend to 
> use virtualization for a small business?
> 
> Thanking you in advance for your efforts in helping me.

Hi Srini,

You can get commercial support for Xen through Xen Source.  Xen also has 
lots of corporate backing including Intel, AMD, and Microsoft.  However, 
Xen relies on paravirtualization which means the guest operating systems 
need to be modified to cooperate with Xen.  In the context of Linux, 
this is no problem and it's easy to get linux guests running inside Xen. 
  However, windows is not yet available as a Xen guest (hopefully soon). 
  VMWare uses a different approach where it modifies the binary image in 
memory, allowing you to run pretty much any OS unmodified.  This is 
slower but more flexible for legacy OSes.  So, if you absolutely need to 
run windows on one of your VMs Xen may not be the right choice at present.

The reason you have to fiddle with the OS is because the x86 has not 
traditionally been designed to be compatible with virtualization.  Now 
that Intel and AMD have introduced virtualization-friendly extensions in 
their latest chips, I would expect these restrictions to change.  Also, 
if you do purchase a system that you plan to run a VMM on, make sure it 
has a CPU that supports these extensions.

Documentation for Xen is available here:
http://www.cl.cam.ac.uk/research/srg/netos/xen/documentation.html

Best of luck,
  - jim.

-- 
James Dinan <dinan at cse.ohio-state.edu>

Graduate RA - Computer Science and Engineering
               The Ohio State University