SQLIO seems like a useful tool. I thought it would be interesting to try to measure the speed difference between a physical disk and a VHD. So I ran SQLIO on the Hyper-V host on the physical drive. Results seemed reasonable. Then I ran it from the guest to test the vhd (on the same physical disk). I expected it to be a bit slower. But instead it was way faster - like 0ms average latency.

So I'm trying to learn something here. It seems like hyper-v is fooling SQLIO somehow but I don't understand it well enough to figure it out.

It's a dynamic vhd, no snapshots or anything, and the vhd is the only file on the disk. The physical disk is actually a two SAS drive RAID 1.