I was asked this by a university in San Diego. 

What are the supported Lync roles that can be virtualized?

All Lync Server 2010 roles can be virtualized.  Here is a list of supported roles:

· Instant Messaging (IM)

· IM conferencing

· Presence

· Enterprise Voice (PSTN)

· Audio Conferencing

· Video Conferencing

· Web Conferencing

· Application Sharing

· Remote Access, Federation (Edge Server)

· Response Group service

Can I virtualize an SBA?

No, an SBA is typically an appliance and cannot be virtualized.

Which are supported Hypervisors for Lync?

· Windows Server 2008 R2 Hyper-V (For details about hotfix, see Microsoft Knowledge Base article 981836, “Network connection is lost on a Windows Server 2003-based Hyper-V VM” at http://go.microsoft.com/fwlink/?LinkId=201212)

· Microsoft® Hyper-V™ Server 2008 R2 Hyper-V (For details about hotfix, see Microsoft Knowledge Base article 981836, “Network connection is lost on a Windows Server 2003-based Hyper-V VM” at http://go.microsoft.com/fwlink/?LinkId=201212)

· VMware ESX 4.0

Does that include Windows Server 2008 Hyper-V?

No, only Windows Server 2008 R2 has been tested and optimized for Lync.  I would recommend also installing Windows Server 2008 R2 SP1 since it includes some new dynamic memory management components.

What guest OS can I use for Lync VMs?

The only guest OS that is supported for a Lync VM is Windows Server 2008 R2.

What type of guest storage is supported?

Fixed VHD or pass through.

Can I mix virtual and physical role servers in the same pool?

It is not recommended to do this because VMs vs. Physical may not provide a consistent experience from a load balancing perspective. You can mix physical and virtual such as SQL physical servers, edge physical servers, front end virtual servers, conferencing virtual servers or any combination listed.

What about Live Migration and Vmotion support?

Not supported and should not be used as a substitute for high availability with Lync (multiple front ends, clustered SQL backends , etc)

What about oversubscription?

Oversubscription is not supported.

What type of overhead is there?

The rule of thumb is to add 10% perf hit for guest VMs. Other limits may include virtual proc limits – e.g. max of 4 procs in VM when 8 procs are recommended which will knock your sizing of Lync down by 50%.

What is a physical vs. virtual sizing chart? note: this is based on a 4 core VM and it can be more cores depending on hypervisor

(chart from Lync virtualization whitepaper here)

Feature definition:

IM&P = IM and Presence

AS = Application Sharing

AV = A/V Conferencing (collocated if Front End Server)

EV = Enterprise Voice (Response Group Service/PSTN access), Mediation Server

Reg = Registrar (subset of IM&P)

AP = Access Proxy (Edge Server)

DP = Data Proxy (Edge Server)

MR = Media Relay (Edge Server)

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What is the max conference size in a VM?

The max conf size drops from 250 physical to 125 virtual when using a 4 core VM.

Can I really scale voice in a VM?

Yes, Miercom was able to stress test Lync voice all the way up to 4.1 million consecutive calls without failure all against a virtualized Lync environment. See test results here.

Should I virtualize or go physical for Lync?

I have had customers do both for their production Lync deployments with equal success. I think as long as you follow the guidelines in the Lync virtualization whitepaper and understand some of the limitations with Lync when you virtualize you can have success.