What are the limitations of Virtual Machines (VMs) created in Windows Server 2012 Hyper-V?
VMs created by Windows Server 2012 Hyper-V are much more scalable than VMs created by earlier versions of Hyper-V. They're more capable in just about every area, ranging from the number of virtual processors supported to the number of VMs per cluster. Refer to the following bulleted list for some of the most striking differences between VMs created by Server 2012 Hyper-V and Server 2008 R2 Hyper-V (with values for the latter shown in brackets).
- Virtual processors per VM: 64 
- Logical processors in hardware: 320 
- Physical memory per host: 4 TB [1 TB]
- Memory per VM: [1 TB] [64 GB]
- Nodes in a cluster: 64 
- VMs in a cluster: 8000 [1,000]
- Active VMs: 1,024 
Windows Server 2012 Hyper-V introduces dozens of other new features as well, including shared-nothing live migration, Hyper-V replica, and more scalability features in just about every dimension. Check out our interview with Microsoft's Matt McSpirit and Edwin Yuen for more information on the changes and improvements, or read Niklas Akerlund's deep dive into some of the most noteworthy new features in his article about managing virtual machines with Windows Server 2012 Hyper-V.
Microsoft's Jeff Woolsey outlined some of the other enhancements during his portion of the Microsoft TechEd 2012 keynote address:
"Well, today, we want to redefine performance, we want to redefine scale. So, today, with Server 2012 and Hyper-V we'll support up to 320 logical processors per server, up to 4 terabytes of memory per server, and up to 64 virtual processors per VM. In addition, you can see we support I've got 100 gigabytes of memory allocated to this virtual machine, but we'll support up to a full terabyte of memory for a VM. And whether this VM has been allocated 10 gigabytes, 100 gigabytes or a full terabyte, it still costs the same. In terms of virtual storage our virtual disks now support up to 64 terabytes per virtual disk. That's 32 times anyone else in the industry. We also support the largest clusters with 64 nodes and up to 4,000 virtual machines in a single cluster."
For more information about the differences between Hyper-V in Windows Server 2008 R2 and Windows Server 2012, see the article "Top 10 Features in Windows Server 2012."