Imagine the following scenario:
You have a Windows Server 2012 hosting Active Directory. The Active Directory database is resident on disks with a cache but no battery backup. Now in the case of lets say a power failure your going to lose any changes that were in the cache and possibly find your yourself with a corrupt Active Directory database. Basically dont’ put active directory (or any other database for that matter) on cached disks without battery backup. If this is the case you should receive warning events in your Active Directory server event log.
Now the same is applicable for Hyper-V. An Active Directory server running on Hyper-V must have disk cache disabled. In the case of a Windows Server 2012 Active Directory on a Windows Server 2012 Hyper-V host the Active Directory server will automatically request disk cache to be disabled. The Hyper-V Host should disable disk cache.
However a bug has been found where the Active Directory Server will request the cache disable and the Hyper-V host will acknowledge this request, however the acknowledgment is actually in error and in reality the cache is still active.
To resolve this issue you need to install rollup 2855336 on the Hyper-V host and perform a quick restart of the host (If you have a cluster you can use cluster aware updating to achieve this with no downtime).
You can download the rollup from here or from Microsoft Update.