CSV block cache causes poor performance of virtual machines on Windows Server 2012

Applies to: Hyper-V Server 2012Hyper-V Server 2012Windows Server 2012 Datacenter


Consider the following scenario:
  • You have Hyper-V virtual machines (VM) that are configured on Windows Server 2012 Hyper-V Cluster by using Scale Out File Server as the Storage Solution.
  • The virtual machine .vhdx files are held in Cluster Shared Volume (CSV).
  • CSV Block Cache is enabled on the volume.
In this scenario, virtual machines may experience slow performance.


Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix Download Available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft website: Note The "Hotfix Download Available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


To apply this hotfix, you must be running Windows Server 2012.

Registry information

To apply this hotfix, you do not have to make any changes to the registry.

Restart requirement

You do not have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
Note The following PowerShell command may be used to view if CSV block cache is enabled or not on a particular CSV volume:

PS C:\temp> Get-ClusterSharedVolume “OS_0002” | Get-ClusterParameter CsvEnableBlockCache 

Object Name Value Type
------ ---- ----- ----
OS_0002 CsvEnableBlockCache 1 UInt32