Many ID 129 events are logged when you run a Windows Server 2012 R2 virtual machine in Windows Azure

Applies to: Windows Server 2012 R2 Standard


When you run a Windows Server 2012 R2 virtual machine in Windows Azure, the event log may fill with many event ID 129 events. Event 129 is logged when I/O requests are dropped because of time-out issues.

Note Event 129 typically means that something is wrong with the disk or that there are faulty logical unit numbers (LUNs). However, in this case, these ID 129 events are harmless.


Hotfix information

A supported hotfix is available from Microsoft Support. 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 the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

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, contact 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, go to 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 update in Windows 8.1 or Windows Server 2012 R2, you must first have update 2919355 installed.

Restart requirement

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

Hotfix replacement information

This hotfix does not replace any previously released hotfix.


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

More Information

During the cloud platform system (CPS) time frame, a new feature was introduced in the classpnp.sys process. This new feature implements an I/O Control (IOCTL) mechanism to enable upper driver layers to set the I/O time-out value and maximum retry count. Spaceport sets the I/O time-out to 10 seconds and allows for no retry. This policy does not work on VHDs, because these may take more time for I/O completion. This fix restricts the calling IOCTL_STORAGE_DEVICE_ERROR_HANDLING to Bus Type SAS, where the disk manufacturer or product ID is not VHD.


Learn about the terminology that Microsoft uses to describe software updates.