WINDOWS 2008 / 2008 R2, HYPER-V & FAILOVER CLUSTERING Better Together.
Updated cluster limits for Hyper-V R2.
Until May 2010, the support limit was 64 VMs per host and up to 16 nodes in a cluster with one node for failover (a 15+1 cluster) for a total of 960 VMs.
In June 2010, the Failover Cluster team upped the support limit to 384 virtual machines per node to match the Hyper-V maximum of up to 384 virtual machines per server.
In addition, the overall number of running VMs per cluster has been bumped to 1000 VMs in a cluster.
We now support up to 1000 VMs in a cluster, whether that’s a:
· 5 node cluster (4 active nodes each running 250 VMs + 1 failover node)
· 11 node cluster (10 active nodes each running 100 + 1 failover node)
Here’s a quick table:
Number of Nodes in Cluster
Max Number of VMs per Node
Max # VMs in Cluster
2 Nodes (1 active + 1 failover)
3 Nodes (2 active + 1 failover)
4 Nodes (3 active + 1 failover)
5 Nodes (4 active + 1 failover)
6 Nodes (5 active + 1 failover)
7 Nodes (6 active + 1 failover)
8 Nodes (7 active + 1 failover)
9 Nodes (8 active + 1 failover)
10 Nodes (9 active + 1 failover)
11 Nodes (10 active + 1 failover)
12 Nodes (11 active + 1 failover)
13 Nodes (12 active + 1 failover)
14 Nodes (13 active + 1 failover)
15 Nodes (14 active + 1 failover)
16 Nodes (15 active + 1 failover)
Increasing the number of VMs of per node only magnifies the need to perform proper capacity planning that takes into consideration the capabilities of the hardware and storage to host VMs and the total resources that the individual VMs require while still having enough reserve capacity to host VMs in the event of a node failure to prevent over commit.
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).
Nodes per cluster
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 cluster and 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.