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Hyper-V R2 to support more clustered VMs – right now

Amidst all the talk about dynamic memory and Windows Server 2008 R2 SP1, one recent virtualization update has managed to fly under the radar – and it actually has nothing to do with the upcoming service pack. Though few seemed to notice, Microsoft recently announced that it has increased the number of virtual machines supported by Hyper-V R2 in a cluster.

As of R2, Hyper-V supported up to 384 VMs per server. That number dropped to 64, however, if those virtual machines were running in a cluster. Microsoft has updated Hyper-V to allow clustered nodes to also support a maximum of 384 virtual machines. The total number of VMs per cluster has also been increased to 1,000 (up from an initial limit of 960).

Jeff Woolsey, Microsoft principal group program manager for server virtualization, said during a conference call that additional testing was required to increase these limits, but that increasing the number of supported VMs in a cluster was a priority based on customer feedback. “Now people can really cram as many VMs as they want onto a single server and get maximum density,” he said.

The maximum number of nodes per cluster remains at 16. IT pros can decide for themselves how many VMs to run per node, a number that will vary depending on how many nodes they have in their cluster. For example, a three-node cluster (two active, one failover) can run up to the maximum 384 VMs per node for a max total of 768 VMs in the cluster. A five-node (four active, one failover) cluster, however, could have each node running 250 VMs to reach the max of 1,000.

Confused? Microsoft provides a table to help clear up some of the bewilderment (and hopefully give your calculator a break). The takeaway here, however, is that the number of clustered VMs that Hyper-V can support has gone up, and the update is already available for R2 (i.e. it’s not part of SP1).

Woolsey said the company isn’t finished upping these limits. “Scalability is one of those areas that’s never really done. So it’s something that you’ll always see us work on, so we can continue to see those scalability numbers climb,” he said.

One Microsoft MVP I spoke to said he’s pleased with the continued improvements that have been made to Hyper-V, both for R2 and since. “They are working hard, there’s no doubt,” he said. “And [Hyper-V] is really coming along.”

He also noted that the new dynamic memory improvements will help with the capacity planning process for this increase in clustered VM support. He stressed, however, that the company is still behind VMware when it comes to other memory management features, such as bubble memory capabilities.

For more information on Microsoft Hyper-V R2, visit

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