Hotfix: Hyper-V backup can cause slow system boot / large registry files

Hotfix: Hyper-V backup can cause slow system boot / large registry files

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A while ago I made an open offer to people to contact me if they had experienced issues using Hyper-V backup.  A number of you contacted me with reports of large registry files in the parent partition – that would slow down system boot over time.

Well, after a lot of investigation we have figured out the cause and a hotfix is now available.  You can download it from here:

http://support.microsoft.com/kb/982210

I recommend that if you are using backup regularly on Hyper-V that you install this hotfix.

Note – that despite the title of the KB article, this fix applies to Windows Server 2008 R2 (not Windows Server 2008).

So what was the cause of the problem?

A short description is as follows:

Whenever we backup a virtual machine using VSS, we momentarily connect the backup copy of the virtual machines virtual hard disks to the parent partition in order to clean them up after backup.  Unfortunately with Windows Server 2008 R2 a new plug-and-play entry would get created in the Windows registry each time that we did this.  Over time this would cause the registry to get larger and larger, which would in turn slow down the Windows boot process.

Cheers,
Ben

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  • Where can i found devnodeclean command to clean registry entries regularly on Win2k8 R2 with Hyper-V installed as stated in support.microsoft.com/.../982210

  • The hotfix is not available for download.  Requires a support call.

    Likewise, the devnodeclean tool is also not available for download.  If you click through to KB 934234, you find the source code (!) rather than an executable.  The source code doesn't even compile right off the bat, but even after you fix the errors, it still doesn't work.  Gives "Error 0x770A11B0 removing phantom."

  • This problem, or something very similar, happens in Windows 2008 server (not R2) also.  Is Microsoft going to provide a fix for this issue?  My server eventually got to the point of booting up and running, but any attempt to login just stayed at the Welcome screen.  I'm rebuilding it now.  This all started with long boot process (several hours), huge registry files (360MB) and over 37,000 entries in the VolumeSnapshot area of the registry.  I figured my problem was related more to backing up with DPM as that was my main backup method.

  • Hotfix is now available.  Looks like I jumped the gun by a few minutes.

    After installing the hotfix, the registry entries that have already been created are not removed.  The devnodeclean tool needs to be made available for cleanup.

  • This affects the 2008 servers as well.  Can this not be used on it? Also I need to be able to clean up the mess this made.

  • IL -

    Unfortunately you can only get devnodeclean by contacting Microsoft product support.

    Tom -

    Glad to hear you were able to download the update.

    Tom Holmlund / Zac -

    There is a different issue with 2008.  This fix only applies to 2008 R2.

    Cheers,

    Ben

  • Are there plans to release this for 2008 and/or a way to clean it up?  Whats the best route to go for requesting devnodeclean?  Thanks

  • Should this hotfix be installed on the Host Server, Guest VM or Backup (DPM) server?  All three?  Just trying to determine where the entries are being created.

  • Zac -

    We are looking into this, but I cannot make any commitments.

    Hoyty -

    This is just for the host.

    Cheers,

    Ben

  • Hi.  I just found this.  We have the same exact issue with two "non R2" virtual hosts.

    Microsoft tech support is stumped, and have been stumped for 2 months.  They did point out the growing registry issues.

    Is there any hope for the non r2 folks, or do we just need to upgrade to R2?

    Is there a registry clean up tool or a manual fix for 2008 non r2?

    Thanks.

  • WE applied the hotfix to 3 of our R2 servers (we have many more). We haven't rebooted 2 of them but one would hang at 32% complete on Configuring Windows Updates for about 10 minutes prior to shutting down the rest of the servers. On reboot, before logging in, it would attempt to do the same thing. So this happened 3 times before we went into safemode. Safemode would say "Failure Configuring Windows Updates. Reverting Changes. Do not turn off your computer." Then it would reboot again. After 3 times, it let us into safemode. We removed the reboot.xml from the C:\windows\winsxs and were able to boot back into the system. But the issue was not resolved. The system still takes 1-2 hours to load up. Another one of servers takes 3-4 hours to load up. All of these servers have been backing up the VMS every hour for several months.

    Is there anyway we can apply to get the devnodeclean utility to clean the system for now until we figure out what to do about the hotfix issue?

  • Hi Ben, what exactly are users running Server 2008 (not R2) supposed to do? The same issue appears to be happening on it as well, is there a hotfix going to be available for Windows Server 2008 only?

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