This weekend I began moving all of our Virtual Server 2005 VHDs to our new Windows 2008 Hyper-v server. Overall the process went smooth with one exception. Large file copies became extremely slow after the installation of Hyper-v.

Prior to installing Hyper-v on the Windows 2008 server, I copied a 16+GB vhd to the Windows 2008 server which took about 25 minutes. Next, I installed Hyper-v and performed the same file copy operation and the speeds diminished to about 65k per second or slower. Hyper-v makes several changes to the networking configurations of the physical host so I began my investigation there but it resulted in no clear indication of why the process slowed. I tried several of the typical options like robocopy, teracopy and eseutil all without any better results.

In the end, I uninstalled Hyper-v and the copied all of the VHDs to the server that I was upgrading then reinstalled Hyper-v. This worked. When I get time I'd like to test to see if the issue still exists now that Hyper-v has been reinstalled or if the issue was limited to that initial installation.