Microsoft did an important change for Windows 2008 R2 Hyper-V Clustering limitations.

To effectively plan for and deploy Hyper-V in Windows Server 2008 R2, you should understand the requirements and maximum configurations for the physical and virtual hardware that will comprise the virtualized server computing environment. You will need to consider the maximums that apply to each virtual machine as well as those that apply to the physical computer that runs the Hyper-V role.

Failover Clusters and Hyper-V

The following table lists the maximums that apply to highly available servers running Hyper-V. It is important to do capacity planning to ensure that there will be enough hardware resources to run all the virtual machines in a clustered environment. For more information about requirements for failover clusters and Hyper-V, see Hyper-V: Using Hyper-V and Failover Clustering (http://go.microsoft.com/fwlink/?LinkID=129063).

Component Maximum Notes
Nodes per cluster 16 Consider the number of nodes you want to reserve for failover, as well as maintenance tasks such as applying updates. We recommend that you plan for enough resources to allow for 1 node to be reserved for failover, which means it remains idle until another node is failed over to it. (This is sometimes referred to as a passive node.) You can increase this number if you want to reserve additional nodes. There is no recommended ratio or multiplier of reserved nodes to active nodes; the only specific requirement is that the total number of nodes in a cluster cannot exceed the maximum of 16.
Running virtual machines per node 1,000 per cluster, with a maximum of 384 on any one node Several factors can affect the real number of virtual machines that can be run at the same time on one node, such as:
  • Amount of physical memory being used by each virtual machine.
  • Networking and storage bandwidth.
  • Number of disk spindles, which affects disk I/O performance.


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