Figure 4.1 An error occurs as the administrator tries to disable write caching within a
virtual machine. Applications would receive a similar error condition.
When applications try to disable write caching on a virtual disk connected to an IDE
controller, no error is returned. This makes the application think that write caching
has successfully been disabled, so no other actions to ensure data integrity are taken.
In reality, though, write caching was not disabled. This can lead to data corruptions in
the event of unplanned outages.
Windows Server 2012 R2 and above do not have this problem, and the good news for
Windows Server 2012 and Windows Server 2008 R2 Hyper-V environments is that
Microsoft released a fix, KB2853952. Once this fix is applied to the Hyper-V host, it
will correctly return a failure error to the VM if write caching is disabled on the IDE
controller, allowing the applications then to leverage FUA.
As you move forward with Windows Server 2012 R2 and generation 2 virtual
machines, you don’t have many choices to make: You will use a virtual SCSI
controller, and you will use VHDX files for the best set of features and scalability.
Common VHDX Maintenance Actions
In Chapter 2, I covered basic commands to create VHDX files and also the basic Edit
Disk actions that allow certain modifications and optimizations to be performed. I
provide additional details in this section.
First, as mentioned, a VHDX file can be natively mounted in Windows Server by right-
clicking it and selecting the Mount option or by double-clicking the file. To unmount,
right-click the volume in File Explorer and choose Eject. This can also be performed
using the various disk management tools, but for automation, scripting the mount and