How many users can a Lync pool hold? This question has come up a few times on the TechNet forums recently and I wanted to talk about it a little.
It’s referenced time and time again that the supported limit to a Lync Server Front End Pool is 80,000 users.
For Lync 2013: “The maximum number of users per pool is 80,000, with twelve Front End Servers. “: http://technet.microsoft.com/en-us/library/gg425939.aspx
For Lync 2010: “The maximum number of users per pool is 80,000, with eight Front End Servers. “: http://technet.microsoft.com/en-us/library/gg425939(v=ocs.14).aspx
If your pool is a part of a pool pairing team, the number would be reduced as you wouldn’t want to invoke failover and end up with 160,000 users in a pool. The why of this can be found by reviewing the capacity planning guides. It’s effectively based upon tested and expected modality usages when run on recommended hardware: http://technet.microsoft.com/en-us/library/gg615015.aspx
The question that comes up on TechNet isn’t just “What’s supported”, it’s “What’s possible”? Is this a hard limit? People have been asking if Lync is used for just pure IM and presence, could you get away with more? The technical answer is yes. The limit is a supported limit only as you can see from the following lab screenshot where I’m querying the total number of users in a single pool.
Hopefully you didn’t stop reading there and run off to build your enormous pool. My strong suggestion is, despite what is possible, if you’re running Lync for this amount of users you should absolutely want to stay within supported parameters. The last thing you’ll ever want to hear when tens of thousands of users are down and you’re scrambling is that you’re not running a supported configuration. On the flip side, if you find yourself at 79,999 users, you’re not going to crash Lync by hiring and enabling two more employees, so take your time and build your new pool properly.