Server 2008 Hyper-V: How’s Your HAL?

Last time, we were wrestling with the issue of getting a migrated Virtual Machine working with the Hyper-V "Integration Services." You may recall that I was not having much success - the mouse integration was not happening, nor was I able to get the latest network adapter to work. In fact, I now believe that none of the VMBus drivers were working. (These special, so-called "synthetic" drivers allow the guest OS to communicate with underlying hardware via a high-speed bus that represents a more direct path to the hardware than the older virtualization products, which routed hardware I/O through the host operating system.)

Well I just couldn't leave it alone, so I got a good night's sleep, came back to the problem the next day, and decided to tackle it afresh. One thing I noticed inside the Server 2008 VM was that Device Manager was reporting a bang on the VMBus device, complaining that the device could not find enough free resources. Some serious Googling revealed Knowledge Base article 954282 (6/26/08), which states that the VMBus will not initialize if it doesn't see the correct Hardware Abstraction Layer, or HAL. (You can view the HAL in Device Manager under the Computer object.) Apparently if you have the "Advanced Configuration and Power Interface (ACPI) PC", you're toast. What you want is the "ACPI x86-based PC." (Yeah, I'm not real clear on the difference either.)

So how to change the HAL? There are a couple of ways to do it, including the command-line tool BCDEDIT, but the simplest is to fire up MSCONFIG, click the Boot tab, click Advanced, and select the checkbox for "Detect HAL." This will add a nanosecond or two to the boot process, and forces the VM to auto-detect the HAL during startup. It's good to leave the autodetection in place, in my view, because it means your VM will boot if you ever need to fire it up again in Virtual Server 2005 or Virtual PC 2007.

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