[CentOS] Server Virtualization

Steven Haigh netwiz at crc.id.au
Mon Sep 17 23:35:27 UTC 2007

Quoting Clint Dilks <clintd at scms.waikato.ac.nz>:
> Hello,
> I work for a school in a New Zealand university and we are wanting to
> implement Server Virtualization for both CentOS and Windows systems.
> So I thought I would ask here what experience people have had with this
> and what issues that you all think should be considered?

Xen is great - however you will need Full virtualisation support in  
your hardware. These are shown as the ?vmx? flag for Intel or ?svm?  
for AMD CPUs in /proc/cpuinfo.

If you are running Windows guest in a linux Xen domain, you will want  
to pay for the Xen licenses. This gives you access to the windows  
drivers for disk and network etc - which improves performance immensely.

> From my own research it seems that VMWare or Xen are really the two
> major products to be considered, are there any others I should be
> considering ?

I can only really speak for Xen...

> Is anyone running Linux "Guest" O/S's inside a Windows host ??  And if
> so can you share your reasons for this?

I'd say VMWare would be the way to do this - if you really had to.

> Anyway thank you for your time and any experiences / knowledge you are
> willing to share :)

The learning curve for Xen is huge. I would suggest a few things  
though if you decide to use it.

1) Setup your Dom0 (the host) disk to use LVM. You will want to make  
MANY partitions. Use a raw disk partition for disk access instead of a  
file as the disk - performance is much better this way.

2) If you're going to add Windows as a guest OS, make sure you get the  
Windows drivers. This is something you have to pay for, but the  
performance increase will be well worth it.

3) use 'xm top' on Dom0 to monitor what your guest systems are doing.  
Get yourself a multi processor system, and divide up usage between  
physical CPUs. This way, you get the best usage of your hardware.

4) Get lots and lots of RAM. We use systems with 8Gb RAM. We give the  
hypervisor 256Mb, and then chunks of 256Mb, 512Mb or 1Gb to each DomU  
depending on usage.

Steven Haigh

Email: netwiz at crc.id.au
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897

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