We have a 4-core physical server happily running along with Win2k3, IIS6, and SQL Server 2k5. Our service provider would like us to P2V the box to ESX. We are not opposed to it, but I've gotten really comfortable with assessing performance on the physical server and feel a bit squeamish about how the virtual replacement will be configured and perform. My quesitons:

  1. The box is multi-slot, 4-core - what will the O/S 'think' it has for CPU? Will this make Windows want to re-register?

  2. How will the performance compare? IIS and SQL love lots of cores and each is <10% on the physical box now. What will VMWare do with that?

Thanks in advance to all for your thoughts.


The OS will think it has how ever many CPU it is assigned in ESX. This can be 1, 2, or 4 virtual CPU. I think in vSphere this has been raised to 8.

It is possible that Windows will want to reregister because every piece of hardware will change. That's a simple thing to fix though.

Performance should not be an issue. I run a 300 person Exchange server on a 2 virtual CPU virtual machine with no issues. You may find also that the VM performs just as well with less virtual CPU because for each virtual CPU you have to coordinate a physical core being read to process a tick. The more virtual CPUs, the more cores that have to be "free". We run most servers with 1 virtual CPU unless there is an absolute need for more. SQL and Exchange are the only machines we run currently with 2 virtual CPU (including Citrix).


See this great article: http://www.vmware.com/resources/techresources/1007

But are you saying you are taking the existing box and making it ESX or moving the existing "server" off the current hardware and onto another ESX host somewhere? When you say "P2V" it it makes me think the latter.

  • Actually, the former. We have a physical box that will be virtualized - P2V. – n8wrl Jun 4 '09 at 18:27
  • OK confused again. That's actually the latter (of my statement). You are doing this: the existing box is being converted to a Virtual Machine that will reside on an ESX host (that is another piece of hardware). Is that correct? – TheCleaner Jun 4 '09 at 19:33
  • Yes that is correct. I'm sorry for the confusion. I was confused by your 2nd statement - 'current hardware' == existing physical server. – n8wrl Jun 4 '09 at 19:58
  • 1
    Understand...yeah you should be fine as stated above. Definitely read the article. It's interesting actually even if you give the VM 4 CPUs to use ESX may actually utilize more of the physical procs as it virtualizes the processing. It's odd and hard to even describe, but I've noticed that it's barely any difference changing that setting from 1 to 2 to 4 cpu. All that really does (in my understanding) is tell ESX that VM needs to have 4 cpu "available" to it at any given time...to make sure other VM's don't hog the procs at the same time. – TheCleaner Jun 4 '09 at 20:23

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