Microsoft, which eats its own dog food since the Virtual Server 2005 era, just announced the complete migration of both MSDN and TechNet, two of the most popular web sites in the world, on virtual machines.

Microsoft kept the back-end database on physical boxes, but moved 100% of its IIS7 frond-ends on Hyper-V RC0 VMs with 4 virtual CPUs and 10GB RAM.
The virtualization hosts (no mention of the brand obviously) are powered by 2 Intel quad-core CPUs and 32GB RAM (2GB are reserved for the Windows Server 2008 parent partition).

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The performance report after this migration is very interesting:

§ Hyper-V CPU overhead (as measured by the parent partition utilization) was 5% to 6% with linear progression as the number of requests increased.

§ CPU oversubscription (three four-processor VMs on an eight-processor physical server) resulted in 3% lower overall performance per physical server based on overall requests per second per 1 percent CPU.

§ Requests per second per 1% CPU performance of MSDN over the previous physical server platform improved. This demonstrates to us the viability of efficient consolidation from dedicated older physical servers to shared virtualized platforms.

§ Physical MSDN handled 21% more requests per second per 1% CPU than virtualized MSDN.

Since this data would be much more meaningful knowing some details about the guest OS workloads (which are not published), virtualization.info reached Microsoft and received the following numbers:

§ the MSDN front-end serves more than 3 million page views per day

§ the TechNet front-end serves more than 1 million page views per day

Read the whole report here.