I have a setup with a Windows 2008 R2 Hyper-V Server and a couple of guests. Yesterday I noticed that one of the guests had become very slow (e.g. noticable lag when browsing through folders). I decided to attempt a restart and at the same apply all new Windows Updates. As it turned out, that took a very long time... Now the server is starting and it is performing "the registry update step of Windows Update", but it is taking forever (or a very long time at least).

The Hyper-V manager reports about 25-50% CPU usage for that machine, but in the Task Manager of the host OS it says 1-5% ?? (which is mostly consumed by the Virtual Machine Worker process). That makes no sense to me. The guest machine had a 50% CPU reserve and limit, which I have now been upped to 100% (made no difference). The server has previously been running smoothly and afaik there have been no changes to the OS/software. The host machine has also been restarted and have had all Windows Updates installed. The host machine itself runs smoothly.

There is also a Windows XP developer guest machine running on the host. That machine runs perfectly fine. If I e.g. fire up VS.NET on it, the CPU-usage will be around 5-40% while starting, and the host OS CPU consumption roughly follows that of the guest (as you would expect).

Does anyone have a clue what could be causing this?

Host OS: Windows 2008 R2 Hyper-V (standard ed.)

Guest OS: Windows 2008 (standard ed.)

Hardware: HP ML350 G5


I wouldn't expect the parent partition CPU usage to track to the guest at all.

The guest CPU usage is accurate as far as the guest perceives it, within the virtualized environment. The "host" in Hyper-V isn't actually a host, and while the RAM numbers reported by it in Task Manager are true, I think you'll find the CPU figures are specific to the host itself.

See this answer (which agrees with me).

Did anything change about the host prior to this slow performance problem? (New graphics driver installed?)

Did anything change about the storage medium for the virtual machine, as it sounds like it could be IO related.

If nothing changed, but something changed - could antivirus be interfering with the VM or its VHDs?

Finally, I've found ResMon.exe on the parent partition to tell me what the VMs are doing in terms of disk IO to VHDs is another workable approach.

  • Thanks Tristan. I'll just split this into a few comments. IO: I'm fairly sure it is not IO related. If I copy a large file locally on the guest it writes at 10-20 MB/sec, which is ok, considering it is both reading and writing form the same disk. Jan 13 '12 at 10:54
  • "change about the host prior to this slow": The problem is I'm not 100% sure when the slow-down actually occured, since it is only slightly sluggish when accessing IIS (serving an IIS page is not that CPU intensive). Jan 13 '12 at 11:01
  • "I think you'll find the CPU figures are specific to the host itself.": What confuses me (among many many other things about Hyper-V ;-) is that there are processes named "Virtual Machine Worker Process" spawned for each server that I start. Jan 13 '12 at 11:11
  • Just got word from our IT-guy that he solved the problem. He ran a "fix Windows Update" script from Microsoft, uninstalled a number of HP management utils and drivers, and disabled some parts of the antivirus (Kasperskys self defense feature). His money is on the AV as having been culprit. Jan 14 '12 at 14:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.