Hyper-V in Windows Server 2012 has some new cool features. While doing some research I found some information about them. Hope it is useful.
Generation 2 VM
The basic architecture of the virtual machine has not changed in a long time. The old BIOS emulation from 1980's is supported by most applications and it is used to emulate the physical hardware the VM' use. The hardware emulated by the hypervisor provides support for hardware, such as a specific NIC card or IDE disk controller. Hyper-V in Windows Server 2012 R2 supports the new UEFI bios option concept of a totally new architecture based on modern hardware with no emulated devices. This makes it possible to add a number of new features, such as secure boot for VMs and booting off virtual SCSI or virtual network adapters. The new Gen 2 VM's are 64bit only and currently limited to Windows 8 and Windows Server 2012 operating systems.
VM Direct Connect
Connecting to a running VM over RDP requires an active Local area network connection, which you can't always have. The VM must have an IP address reachable by the system attempting to connect, this has its own potential management or security issues. VM Direct Connect allows connection via the VM bus. It uses the RDP protocol to connect to the VM. This makes it possible to connect an administer VM's behind firewalls without the need to have direct access to the VM. It's also integrated into the Hyper-V management experience.
Extend replication to a third site
A new feature called Hyper-V Replica in Windows Server 2012 is currently limited to a single replication target. This makes it difficult to support scenarios like a service provider wanting to act both as a target for a customer to replicate and a source to replicate to another offsite facility. Windows Server 2012 R2 and Hyper-V now give the option to replicate to a tertiary site. By the same token, enterprises can now save one replica in-house and push a second replica off-site.
Replication frequency options
Hyper-V Replica in Windows Server 2012 provides a fixed replication interval of 5 minutes. This means you can't replicate any faster, even if you have the hardware to support it. Nor can you replicate any slower, even if you don't need such frequent copies. Two new options have been added in the Windows Server 2012 R2 release to support more frequent (30 seconds) and not so frequent (15 minutes) replication. This will even support an intermittent connection. By default, Hyper-V Replica will look for 12 missed cycles before it switches into a failed state. With the 15-minute cycle, you buy up to three hours of network downtime.
Compression for faster migration
Hyper-V 2012 R2 has two new options to help improve the performance of live migrations. The first is the ability to enable compression on the data. The second option, SMB Direct, requires network adapters that support RDMA. Microsoft's advice: If you have 10Gb available, use RDMA (10x improvement); otherwise, use compression (2x improvement). Compression is the default choice and it works for the large majority of use cases.
Online VM exporting and cloning
One of the downsides of Hyper-V in Windows Server 2012 is the need to stop a running VM before you can export or clone it. In production environments, this is simply not an option. Windows Server 2012 R2 Hyper-V removes this restriction. It's now possible to export or clone a running VM from System Center Virtual Machine Manager 2012 R2 with a few mouse clicks. As with pretty much anything related to managing Windows Server 2012, you can accomplish the same task using Windows PowerShell.
Online VHDX resizing
In Windows Server 2012 Hyper-V, it is not possible to resize a virtual hard disk attached to a running VM. Windows Server 2012 R2 removes this restriction, making it possible to not only expand but even reduce the size of the virtual disk (VHDX format only) without stopping the running VM. What you can't do with this feature: Compress an online VHD. You can make these adjustments from System Center Virtual Machine Manager 2012 R2, Hyper-V Manager, or the command line using PowerShell. You can use PowerShell to set the disk size to the current disk consumption if you want to reduce it to the absolute minimum.
An interesting feature in Windows Server 2012 R2 is the ability to limit individual VMs to a specific level of I/O throughput. You have two settings for minimum and maximum IOPS. In the initial release of Windows Server 2012 R2, the only number that really makes a difference is the maximum limit. The IOPS are measured by monitoring the actual disk rate to and from the attached virtual hard drives. These feature allows administrators to balance storage IOPS across different VM's.
Dynamic Memory support for Linux
Microsoft continues to improve support for Linux VMs. In the Windows Server 2012 R2 release, Hyper-V gains the ability to dynamically expand the amount of memory available to a running VM. This capability is especially handy for any Linux workload (notably Web servers) where the amount of memory needed by the VM changes over time. In environments with many Linux VMs, dynamic memory becomes even more critical to efficiently manage the total memory used by all running VMs. Windows Server 2012 R2 Hyper-V also brings Windows Server backups to Linux guests. In the example the Linux guest starts up with 128MB and can dynamically grow as needed.
A great feature for cluster VM's is the use of a Shared VHDX file instead of the traditional iSCSI or Fibre Channel connectivity to a SAN. The VHDX can be on a CSV volume or a SMB 3.0 fully Windows 2012 Scalable File Share. This allows for SQL virtual clusters or Windows File Share Clusters.
Additional Information can be found at: