In order to rollout a Lync Server 2013 Enterprise Edition Front-End pool, setup of a SQL Server database backend is mandatory. You can deploy either the Standard or Enterprise edition of SQL Server 2008 R2 or SQL Server 2012 but only the 64-bit edition (x64) is supported.
The introduction of high-availability for the database software involves setting up more than one SQL Server computer. This can be achieved with the implementation of native database mirroring or failover clustering. Running with the former configuration brings about several key enhancements to Lync Server that are missing from the latter.
Until recently, SQL failover clustering topology was only officially supported for organizations migrating from an existing Lync Server 2010 infrastructure. According to latest information released on TechNet*, SQL Active/Passive Clustering (up to 16-node setup) is now a supported scenario for Lync Server 2013 greenfield deployments i.e. you do not need to operate a previous version of Lync Server in order to deploy SQL Clustering.
This is a significant and welcome change for organizations that have standardized database deployments based on SQL failover clustering, and may not have tested or approved the use of SQL Mirroring.
To maintain satisfactory performance, other shared SQL instances should not be setup on the passive node. Note that SQL mirroring can be configured directly in Lync 2013 Topology Builder whereas setup(.exe) for SQL Server must be used to deploy SQL failover clustering feature.
Finally, SQL Server 2012 “Always On” feature is still not a supported scenario in Lync Server 2013.
* Database Software Support (link)
Technorati tags: Microsoft Lync Server/Client