The Virtualization team is reporting 87% of native performance when using Dynamically expanding drives.
A number of MVPs were emailing today about best practices for High Availability using Hyper-V and Clustered Shared Volumes. A great topics in and of itself but one that I will bring forward more extensive information in the near future.
A side topic came up. Oliver Sommer, respected MVP from Germany, introduced me to the increased performance of Dynamic Expanding drives in Hyper-V R2. Now this should not be confused with dynamic versus basic drive formats. This is dynamically Expanding Storage versus Fixed storage in Hyper-V.
There was a little uncertainty as to the exact numbers of the performance increase. A little research on my behalf revealed the Virtualization team is reporting 87% of native performance when using Dynamically expanding drives. Source: http://blogs.technet.com/virtualization/archive/2009/07/22/windows-server-2008-r2-hyper-v-server-2008-r2-rtm.aspx
In the end, we still recommend fixed disks for production use with Hyper-V R2 because it pre-allocates disk usage upfront, but if you want to use dynamically expanding virtual hard disks and are willing to take a small performance hit, Hyper-V R2 is a must.