Some 5 years ago, Microsoft bought a third party company (Parlano) and acquired their highly regarded group chat product, which was a feature missing from OCS. Group Chat was eventually “added” into OCS and Lync 2010 although as more of a bolt on than a full citizen in the Lync product. Group chat in those days was essentially a separate stand-alone application that required separate servers for both the GC feature and for its databases. The actual installation was also challenging and highly error prone.
With Lync 2013, Microsoft did a lot of simplification work integrating it into the overall Lync topology. Microsoft also changed the name of this feature to Persistent Chat. With PC in Lync 2013, you can co-locate the GC service on the Front End servers, and you can co-locate the PC databases on SQL servers used for other UC databases.
Like all of the Lync 2012 components, PC is supported by the underlying Lync Architecture, including the high availability features. Like all Lync features, availability requirements tend to be pretty high, as companies begin to depend on things like PC.
In a complex blog post over on TechNet, Richard Schwendiman (an MS Exchange/Lync PFE) presents a deep dive into PC’s High Availability and Disaster Recovery features. Richard starts off by looking at how you can engineer HA in a single data centre. This architecture enables a single PC server to fail and for the client to be re-connected to another PC server. The blog post then goes on to look at disaster recovery – or engineering against the failure of an entire Lync Site, in particular using stretched sites for PC.
This blog post is worth reading if you are going to be implementing Persistent Chat either as part of an initial Lync deployment or as a later phase. TechNet has a good article that provides more information on how Persistent Chat works. You can find more details on HA and DR in Lync Server 2013 here (a blog article by Thomas Binder). And for more information on capacity planning for PC, see the TechNet article at Http://technet.microsoft.com/en-us/library/gg615006.aspx.