Multi core processor machines in a virtualized enviornment
How does the number of processors supported in a virtualized environment affect performance?
The answer to this question really depends on the Operating System (OS) and application stack that will be deployed as a virtual machine. Just like when dealing with physical machines, the OS and applications deployed must be able to take advantage of a multi core processor system to gain any benefit from the multiple processors. If the OS and applications running in the virtual machine support multiple processors, then a virtual machine can be assigned dedicated physical processors enabling it to achieve performance closer to a physical multi core processor machine. This is especially useful for high-end database or application servers that are virtualized.
Currently, VMware ESX 3.0 supports up to four processors dedicated to a single virtual machine, Microsoft Virtual Server 2005 R2 does not support multiple processors for a virtual machine, and XenEnterprise 3.1 supports up to 32 processors per Linux virtual machine guest. However, look for multi-processor support in Microsoft's upcoming hypervisor in Server Longhorn, codename "Viridian," and Windows guest multi-processor support in XenEnterprise 3.2.
This was first published in April 2007