You have a Lync Server 2013 infrastructure that contains an Enterprise Edition front end pool. You plan to add the following server roles to the existing infrastructure:
* Edge Server
* Archiving Server
* Monitoring Server
* Persistent Chat Server
You need to identify the minimum number of Microsoft SQL Server servers that must be added to the existing Lync Server 2013 infrastructure. The solution must not use the existing SQL Server Back End Server. What is the minimum number of SQL Server servers that you should identify?