On the 15th of August 2013, Microsoft released new database support options for Lync 2013. When Lync 2013 was released the only supported database fail over construction was achieved by using SQL mirroring.
The statement from Microsoft for high-availability support for Lync 2013 now is:
Lync Server 2013 supports the user of either SQL mirroring or SQL clustering for each Lync Server database. You can easily set up SQL mirroring with the Topology Builder tool in Lync Server 2013. For SQL failover clustering, you must use SQL Server for setup.
SQL Clustering support is for an active/passive configuration. For performance reasons, the passive node should not be shared by any other SQL instance.
For more information see Technet : Database Software Support.