The July Windows Server 2012/Windows 8 update (KB2855336) contains two fixes for Hyper-V scenarios that are likely to be important to a number of customers.
Both of these updates are included in the rollup KB2855336.
KB2853952 - Loss of consistency with IDE-attached virtual hard disks when a Windows Server 2012-based Hyper-V host server experiences an unplanned restart (renamed from Active Directory database becomes corrupted when a Windows Server 2012-based Hyper-V host server crashes)
This issue effects virtualized active directory servers – in the event that the host crashes or looses power the active directory instance may become corrupted. If this occurs on startup active directory will blue screen/bug check the virtual machine with an error of “c00002e2 Directory Services could not start because of the following error: %hs Error Status: 0x%x. Please shutdown this system and reboot into Directory Services Restore Mode, check the event log for more detailed information.”. There may be additional roles or applications impacted by this issue as the underlying cause is that when a guest operating system requests the Hyper-V server to disable disk caching the wrong error is returned making the guest operating system believe that caching has been disabled when it has not.
This update should be installed on the Hyper-V host.
KB2854362 - Vmms.exe processes freeze on certain nodes in a Windows Server 2012-based Hyper-V failover cluster
This issue effects clustered Hyper-V servers with virtual machines hosted on a scale-out file server cluster. In the event of a node failure that results in VM’s being failed over and brought online on other nodes the VMMS process on those nodes may freeze resulting in VM’s that remain in the offline state.
This update should be installed on all of the Hyper-V hosts within a cluster.
-Program Manager, Hyper-V