and this week I am diving into Lync :-)
Diving in the kelp forests at Catalina or into Lync - same thing!
I recently passed the 74-338 Lync 2013 Depth Support Engineer exam, and this week I am attending a training class on the subject. Good course, and I think I will learn a lot this week. I will try to summarize some questions and good points day-by-day.
Why should we not mix physical and virtual servers in a Lync Enterprise Edition pool?(and why should we not mix physical and virtual server pools in pool paring?)
On page 29 of the paper Planning a Lync Server 2013 Deployment on Virtual Servers we can read:
Mixing physical and virtual servers in the same pool is not a supported configuration.
The reason has not so much to do with the actual virtualization technique, but rather the fact that all servers in a pool should have about similar performance. So it would be just as bad to keep an old slow server in a pool with new high performing servers, users would get inconsistent response times and would maybe complain about this. Even virtual servers should have equal performance capabilities. Also, things like latency and virtual servers competing for resources on a physical host play into this. (The same reasons even apply to pool pairing.)
Some notes on Lync load balancing
Lync uses DNS Load balancing for SIP.
Reading this article on how to Configure DNS for Load Balancing, it states that DNS round robin should be turned on if using a windows DNS server.
However, reading this great old article on DNS Load Balancing in Lync Server 2010, we learn that the order in which these are returned to the client is irrelevant. The client chooses an IP address from the list of returned IP addresses at random.
So, the conclusion must be that for DNS Load Balancing in Lync, using round robin or not on the DNS server does not matter at all.
When building Lync lab environments with Enterprise pools the load balancing of non-SIP traffic in your Lync often poses a problem. However, checkout the Kemp Virtual LoadMaster VLM-2000. It is actually a software based "hardware" load balancer that will run on Hyper-V, and the best part is that as an MCP you get a "Not for resale" license for free for MCPs.