When we talk about changes in the Skype for Business Server 2015, one of the areas that is not new but perhaps is better documented than the previous versions (Lync Server 2013) are the scenarios that are supported and recommendations around pool paring. What we will cover are some basic pool paring scenarios including some of the branch office scenarios with SBA’s and SBS’s. Now you might ask yourself; “If they are so basic, why are you covering it?” The areas I would like to talk about come up quite a bit during customer conversations regarding “What if Disaster Recovery scenarios with additional sites and pools”. To better define the scope of this article we will focus on the following areas:
- Enterprise Edition Server Pool Pairing
- Standard Edition Server Pool Pairing
- Branch Office Appliances Pairing
Enterprise Edition Pool Pairing
To begin with, what has not changed is the 1:1 relationship of the Enterprise Edition Server for Front End Server pool pairing. If I have one Enterprise Edition pool then I can only pair with one other Enterprise Edition End pool. A nice thing is there are no hard and fast rules on where the other pool is located; the other pool can be in the same physical site or dispersed across a geographic location that is another country. Now of course we run into what is practically with regards to users failing over to another continent if their primary pool is not available, but that is another topic of conversation. A common design flaw that I see with many customers is not planning the failover capacity appropriately; what I mean by that is not planning the secondary site (that is currently hosting users too) with enough capacity in case the primary site is unavailable. For example Site A which is running Skype for Business Server Enterprise Edition has 15,000 users and there are three Front End server’s in the pool. Site B has 10,000 users and has three Front End servers. Just right there creates a design problem, for each site A and B should be able to handle all 25,000 users for the entire organization without the addition of more Front End servers. Based on capacity planning the appropriate number of Front End servers each site should have should be four Front End servers for each site, A and B. For additional material on Front End server capacity and planning Determining How Many Front-End Servers to Deploy in Lync Server 2013
Note: The pool paring configuration can still be done in topology builder and managed with the management shell.
Figure 1: Enterprise Edition servers paired in a 1:1 relationship
Standard Edition Pool Pairing
Similar to the Enterprise Edition scenario, the Standard Edition Server follows the same pattern in a deployment where it too is a 1:1 relationship with pool pairing. You can pair a single Standard Edition Server to another Standard Edition Server. Like the Enterprise Edition Server deployment, planning plays a key role in the designing phase for sites. A Standard Edition Servers supports up to 5,000 concurrent users. So if I have two sites, A and B and each site has 4,000 users, then having a single Standard Edition Server deployed per site may not be the best design for the environment in the event that either site needs to failover to the other. Now we are talking about having 8,000 users trying to connect to a single Standard Edition Server which from a user concurrency perspective is not supported by Microsoft. Not to get us off topic and talking about capacity planning, but the approach would be go to an Enterprise Edition deployment for each site in the scenario that I just drew up. As the Enterprise Edition server, the Standard Edition server can also be configured with pool paring in topology builder and managed with the management shell.
Note: When pairing pools make sure to only pair Enterprise with Enterprise and Standard with Standard; don’t mix and match them. Even though there isn’t anything in topology builder that would specifically block you from doing so, for this is not a supported Microsoft best practice.
Figure 2: Standard Edition servers paired in a 1:1 relationship
Branch Office Pool Pairing
Now let’s take a look at the branch office solution incorporated with the Standard or Enterprise Edition pool. No matter what has been deployed, whether it’s a Survival Branch Appliance (SBA) or Survival Branch Server (SBS) the relationship is still a 1: Many relationship with pool paring. So we can have many branch office appliances to a single pool regardless of what edition is running. This solution has not changed from the previous edition which was Lync Server 2013. There isn’t a published specific number of branch appliances that can be paired to a particular pool, irrespective if the pool is Enterprise or Standard. Now there brings about another topic on what provides more feasibility, what would fit better from an operational and from a disaster recovery standpoint.
Note: When pairing pools make sure to only pair Enterprise with Enterprise and Standard with Standard; don’t mix and match them. Even though there isn’t anything in topology builder that would specifically block you from doing so, for this is not a supported Microsoft best practice.
Branch Appliance paired in a 1:1 relationship with an Enterprise Edition Pool.
Note: The scenario of A to B to C doesn’t exist; meaning if you have a pool (A) and pool (B) and a branch site (C). If Pool A and pool B are both paired to each other. If the branch site (C) is paired with pool (A) and pool (A) fails then it users would failover to Pool (B) by design. As for the branch site (C) that was paired to pool (A) then those users would be operate in “limited functionality” mode.
Note: When pairing pools make sure to make sure you pair physical with physical and virtual with virtual. Just like the Standard vs Enterprise recommendation, there isn’t anything in topology builder that is not going to allow you to pair a physical pool to a virtual pool, but this is not supported solution by Microsoft.
To Pair or Not to Pair
Should you pair pools shouldn’t be the question; but how to pair pools properly should be the question. Disaster recovery planning and preparation with Skype for Business Server 2015 is going to be key for plenty of organizations going forward this year and in 2016; and laying out the proper foundation with best practices is a key part to understanding what should if a pool was to ever become unresponsive or unavailable in an environment.
