In a TechNet blog Michael Kleef announced that the number of VM’s per logical processor (LP) has been increased from 8:1 to 12:1, a 50% increase of VM density.
The increased ratio is supported if all guests run Windows 7. This is clearly aimed at Virtual Desktop Infrastructure (VDI) environments on Hyper-V R2. During the keynote of TechNet Europe 2010 we already heard increased VM density per host by at least 40%.
Kleef explains:
VMs/core support implies only physical core support. Logical processors can be either physical or multi threaded cores. As an example, Intels newest Westmere processors support 6 cores, though they are Hyperthreaded, meaning that you actually have 12 logical processors. According to our new support statement this means that on just one of these Westmere processors, we can support up to 144 VMs! Of course this depends on the workload in use but it definitely lifts the game in support.
Currently the supported maximum VM’s of a Hyper-V R2 server or cluster nodes was 384 per server if each guest was configured with 1 virtual processor (vCPU). The ratio is measured against the number of logical processors available to the hypervisor. A host with 8 x 6 cores offers 48 LP’s. With a 8:1 ratio this would entail 384 guests with 1 vCPU.
Please be aware that several other factors including storage I/O and network throughput can easily lower the maximum number of guests per server.
Unfortunately no changes were announced to the maximum number of vCPU’s per guest (still 4) or the maximum number of memory (still 64GB). On the other hand this can change any time. It doesn’t take more than a blog or a tweet to announce these kind of changes. Just like a Windows Update changed the number of supported logical processors from 16 to 24 back in the days of Hyper-V R1. With ever increasing number of cores per processor and growing demand for high performance and scalable virtual machines further changes to the current limits cannot be avoided. It is not a matter of technical limitation but rather of support.
For an interesting Wiki on the concept of vCPU, see Brian Ehlert’s contribution:
http://social.technet.microsoft.com/wiki/contents/articles/hyper-v-concepts-vcpu.aspx
An interesting take on core density and VM’s per logical core is Andre Leibovici’s blog “Cores and more Cores … We don’t need them!”
http://myvirtualcloud.net/?p=1519
