Tim Litton posted a blog about performance optimization for Hyper-V, looking at fixed versus dynamic VHDs. Here’s an excerpt:
The following graph shows the relative performances for a number of different scenarios (with Dynamic VHD being the baseline).
Fixed VHD always performs better than a Dynamic VHD in most scenarios by roughly 10% to 15% with the exception of 4k writes, where Fixed VHD performs significantly better.
Recently, QLogic published a benchmark for I/O throughput for storage devices going through Windows Server 2008 Hyper-V (http://www.qlogic.com/promos/products/hyper-v.aspx) that closely matches the native performance, thus demonstrating Hyper-V’s ability to bring the advantages of virtualization to large-scale datacenters.