In a Front End pool, you should have one Front End Server for every 10,000 users homed in the pool, plus an additional Front End Server to maintain performance when one server is unavailable. The maximum number of users in one Front End pool is 80,000. If you have more than 80,000 users at a site, you can deploy more than one Front End pool.

When you account for the number of users in a Front End pool, include the users homed on Survivable Branch Appliances and Survivable Branch Servers at branch offices that are associated with this Front End pool.

The additional Front End Server helps maintain performance in case one server is unavailable. When an active server is unavailable, its connections are transferred automatically to the other servers in the pool. For example, if you have 30,000 users and three Front End Servers, then if one server is unavailable, the connections of 10,000 users need to be transferred to the other two servers, for an average of 5,000 transfers per server. Additionally, the remaining two servers will each have 15,000 users, which is a larger number than recommended.

However, if you start with four Front End Servers for your 30,000 users and then one is unavailable, a total of 7,500 users will be moved to three other servers, for an average of 2,500 transfers per server, and 10,000 users per server. This is a much more manageable load.

When you have more servers in the pool, the need for this additional server is less important. For example, if you have 80,000 users in the pool, eight servers are generally sufficient. In this case, if one server is unavailable, there will be about 10,000 users moved to 7 other servers, for an average of about 1,400 per server.

The maximum number of users in a Front End pool is 80,000. This is a constraint of the back-end database. The maximum number of Front End Servers in a pool is 10.

For a Front End pool with 80,000 users, eight Front End Servers is sufficient for performance, including failover performance, in typical deployments that follow the Lync Server 2010 User Models. You may want to deploy more than eight Front End Servers in these scenarios:

• The hardware for your Front End Servers does not meet the recommendations in Server Hardware Platforms.
  
  
• Your organization’s usage differs significantly from the user models, such as significantly more conferencing traffic.
  
  
• You are collocating A/V Conferencing Server with Front End Server in a Front End pool of more than 10,000 users.
  
  

The following table shows the average bandwidth for IM and presence, given the user model, as defined in Lync Server 2010 User Models.

Given the user model that 5% of users in a pool may be in a conference at any one time, a pool of 80,000 users could have about 4,000 users in conferences at one time. These conferences are expected to be a mix of media (some IM-only, some IM with audio, some audio/video, for example) and number of participants. There is no hard limit for the actual number of conferences allowed, and actual usage determines the actual performance. For example, if your organization has an unusually large number of mixed-mode conferences with many participants, you might need to deploy more Front End Servers or A/V Conferencing Servers than the recommendations in this document. For details about the assumptions in the user model, see Lync Server 2010 User Models.

The maximum supported conference size hosted by Lync Server is 250 participants. While this large conference is going on, the pool can still support other conferences as well. While a 250-user conference is happening, the pool still supports a total of 5% of pool users in concurrent conferences. For example, in a pool of eight Front End Servers and 80,000 users, while the 250-user conference is happening, Lync Server supports 3,750 other users participating in smaller conferences.

Regardless of the number of users homed on the Front End pool or Standard Edition server, Lync Server supports a minimum of 125 other users participating in smaller conferences while a 250-user conference is happening. For example, on a Standard Edition server with 5,000 users, a 250-user conference can be concurrent with other smaller conferences totaling 125 users.

If you have fewer than 10,000 users at a site, and typical A/V usage, you can collocate the A/V Conferencing Server role with your Front End Servers.

If you have more than 10,000 users, we recommend you deploy A/V Conferencing Server separately from the Front End pool. Assuming usage similar to what is described in Lync Server 2010 User Models, you should deploy one A/V Conferencing Server for each 20,000 users at a site. At a minimum we recommend two A/V Conferencing Servers for high availability.

When you account for the number of users for the A/V Conferencing Servers, include the users homed on Survivable Branch Appliances and Survivable Branch Servers at branch offices that are associated with a Front End pool at this site.

Another guide for A/V Conferencing Server capacity planning is that each A/V Conferencing Server can support about 1,000 concurrent A/V conference users. With the user model assumption of 5% of an organization’s users in concurrent conferences, this leads to the recommendation of one A/V Conferencing Server per 20,000 users at the site. If your organization has a higher or lower percentage of users participating in A/V conferences, you can adjust the number of servers needed in your organization.

You should deploy one Edge Server for every 15,000 users who will access a site remotely. At a minimum we recommend two Edge Servers for high availability.

When you account for the number of users for the Edge Servers, include the users homed on Survivable Branch Appliances and Survivable Branch Servers at branch offices that are associated with a Front End pool at this site.

Note:

To improve the performance of the A/V Conferencing Edge service on your Edge Servers, you should enable receive-side scaling (RSS) on the network adapters on your Edge Servers. RSS enables incoming packets to be handled in parallel by multiple processors on the server. For details, see http://go.microsoft.com/fwlink/?LinkId=206013. For information on how to enable RSS, see your network adapter documentation.

For performance, you should deploy one Director for every 15,000 users who will access a site remotely. At a minimum we recommend two Directors for high availability.

When you account for the number of users for the Directors, include the users homed on Survivable Branch Appliances and Survivable Branch Servers at branch offices that are associated with a Front End pool at this site.

How many Mediation Servers to deploy depends on many factors, including the hardware used for Mediation Server, the number of VoIP users you have, the number of gateway peers that each Mediation Server pool controls, the busy hour traffic through those gateways, and the percentage of calls that are calls that bypass the Mediation Server.

The following tables provide a guideline for how many concurrent calls a Mediation Server can handle. For details about Mediation Server scalability, see Estimating Voice Usage and Traffic and Deployment Guidelines for Mediation Server.

Stand-alone Mediation Server Capacity: 90% Internal Users, 10% External Users

Note:
Although servers with 32 GB of memory were used for performance testing, servers with 16 GB of memory are supported for standalone Mediation Server, and are sufficient to provide the performance shown in this table.

Stand-alone Mediation Server Capacity: 70% Internal Users, 30% External users

Note:
Although servers with 32 GB of memory were used for performance testing, servers with 16 GB of memory are supported for standalone Mediation Server, and are sufficient to provide the performance shown in this table.

Mediation Server Capacity (Mediation Server Collocated with Front End Server)

One Monitoring Server can support up to 250,000 users when Monitoring Server and the Monitoring store are located on the same server and not collocated with other server roles.

One Archiving Server can support up to 500,000 users when Archiving Server and the Archiving store are located on the same server and not collocated with other server roles.

If Monitoring Server and Archiving Server are collocated together, each can support up to 100,000 users. If the number of users allows, a Monitoring Server and Archiving Server at one site each can serve the users at all your central sites and branch offices.

One Standard Edition server can support up to 5,000 users.

• Estimating Voice Usage and Traffic
  
  
• Deployment Guidelines for Mediation Server