Excellent article from the Ask Premier Field Engineering (PFE) Platforms blog on TechNet.
One key config takeaway is that while in Server 2012 RTM Hyper-V you still cannot boot/host an OS from anything other than an IDE based virtual device you should always be adding a virtual SCSI adapter and disk to host any Jet based databases and logs. This would include the placement of Active Directory databases.
Good to note that Hyper-V in Server 2012 R2 along with Gen 2 VM’s will allow boot from SCSI VHD as well as SCSI based virtual DVD.
Some additional reading from the above article: Update Rollups For Windows Server 2012 and Windows 8 Explained