Jeroen’s weblog

Until today I still wasn’t able to install the July CTP of VS.NET 2005 on a VM hosted by Virtual Server 2005 until someone in microsoft.public.virtualserver found the following KB article: Slow performance when you try to access resources on your Virtual Server 2005 host computer from a guest virtual machine, which is exactly my (and many others’) problem. This sure is a relief, as not being able to move large files to/from a VM would have made it completely useless for development/testing.

A quick summary of the article: the virtual NIC implemented in the VM doesn’t support TCP segmentation offloading, so if the underlying physical NIC is configured to use it, a lot of translation is taking place. This slows things down immensely, up to the point where copying large files fails completely (my guess is timeouts). Fortunately, this can be fixed by simply disabling it in the Device Manager (Network adapters -> Your physical adapter -> Properties -> Advanced) on the host machine. I’ve done this today and it’s working like it should, finally!