Lync Server 2013 use SQL Server 2012 Express Edition (64 bit) for servers where Lync server role require local configuration database and SQL Server 2008 R2/2012 (64 bit) for Lync Back End, Archiving, Monitoring, and Persistent Chat and Persistent Chat Compliance databases. You can configure SQL mirror to achieve High Availability for Lync Back End, Archiving, Monitoring, and Persistent Chat and Persistent Chat Compliance databases.

So, now we will have a look into the databases and their uses.

Lync Back End Server databases: Lync Back End (SQL) Server maintains Lync Central Management Store, users & applications databases. You can also use the same database server for archiving, monitoring, persistent chat and persistent chat compliance databases. For more information about the collocation of database please go through http://technet.microsoft.com/en-us/library/gg398102.aspx

SQL Back End server store Central Management Store, users & applications databases for Lync Enterprise Edition FE pool.

Below is the list of backend server databases:

xds: xds is the main database of Lync Server and part of central management store which maintain the topology information, polices, configuration etc. and replicate a read only copy to every subsequent lync server.

lis: lis stand for Location information service and maintains the location information service data.

rtcxds: rtcxds maintains the backup for user data

rtcshared: rtcshared hosts the conferencing directory

rtcab: rtcab stands for real time communication address book and maintain the address book service information

cpsdyn: cpsdyn maintains the dynamic information database for Call Park application.

rgsconfig: rgsconfig maintains the response group configuration service data file.

rgsdyn: rgsconfig maintains the runtime data for response group configuration service data file.

Lync Front End Server Local databases: Lync FE server uses SQL express edition to store databases under database instance name RTC Local. There are three databases (xds, rtc & rtcdyn) under RTC Local which created at the time of Lync Installation on each Front End server and maintain the replica from Lync Bank End Server. In lync 2013 Front End & Back End are loosely coupled and use lazy writes to update the databases. Therefore, Lync 2013 maintains presence information on Lync Front End Servers.

Below is the list of frontend server databases:

xds: xds on Lync frontend server maintain a read only copy of xds database which is part of central management store and resides in SQL backend database server.

rtc: rtc store persistent users data such as contact list, schedule conferences and ACL’s etc.

rtcdyn: rtcdyn maintains dynamic user data such as presence.

lyss: lyss stands for Lync Storage Service and used to maintain HA within a FE pool. It is a blob database and abstract writes to backend database. It maintains a copy of the data within Front End servers in the pool temporarily, and delete that data once it has been delivered to the final database server. It is a replacement for MSMQ which was used in previous version of Lync. Therefore, it is part of the Front End servers and it is located under LYNCLOCAL named instance. It is also used for Archiving integration and Unified Contact Center. Currently, it supports Exchange and SQL for archiving.

Lync Archiving database: Lync 2013 provides two options for archiving. You can use either SQL Server or Exchange Server for archiving purpose. If you use SQL server as an option for archiving it creates LcsLog database for the same.

lcslog: lcslog maintains data file for the retention of instant messaging and conferencing data on an Archiving Server.

Lync Monitoring databases: Lync 2013 maintain call detail recording and quality of service data if you deploy Lync Monitoring Server role in you deployment.

cdr: cdr stands for call detail recording and maintains the call detail recording data.

QoE: QoE stands for quality of Experience and maintains the QoE data to provide best experience to Lync users.

Lync Persistent Chat database: Lync 2013 has new server role called Persistent Chat which is replacement of Group chat server and to maintain user persistent chat data Lync uses mgc database.

Lync Persistent Chat Compliance database: In Lync 2013 as Persistent Chat is a part of Lync Servers role, so to maintain compliance data for this user service Lync uses mgccomp database.