
Dec 18, 2013
High Availability, as defined by SearchDataCenter, “refers to a system or component that is continuously operational for a desirably long length of time.” After migrating voice communications to Microsoft Lync Server 2013, you should provide high availability and disaster recovery procedures to minimise downtime. This ensures that you will achieve the application availability in case of any failure. Today I’ll take a look at some features of Lync Server 2013 that should be taken into consideration when offering high availability such as back-end server databases, file store and branch sites. Lync Server 2013’s architecture of the Enterprise Edition Front End pool has changed as it now offers a distributed systems architecture. Information is kept on the local instances of the front end server – one of which is the master and the other two are replicas. In the previous version of Lync Server, the back end SQL Server was the real time data store, which provided a centralised data store, but it was a performance bottleneck. Now when any change happens, data is published to the central management store which in turn replicates back to all of the front end servers. With this, the front end servers provide an out-of-the-box high availability. The Lync fabric manager is responsible for the data distribution among all the front end servers. It’s also important to consider high availability for back-end server databases. Previously, clustering was the best way to provide high availability for back-end servers, but Lync Server 2013 no longer supports clustering. Instead, Microsoft recommends moving your present high availability model to SQL Server mirroring. Mirroring is asynchronous replication between the primary and mirror server. SQL Server now offers a new feature known as AlwaysOn Availability Group, which is a new version of SQL mirroring. Lync Server 2013 also uses file store, which is basically a file share to store the conferencing content and address book. High availability of the file store also needs to be considered - a Distributed File System (DFS) can be used here. Another consideration is high availability of branch sites. Branch sites should not suffer in the event of the central site failure. There are a number of methods that can be used to ensure branch site resiliency such as an implementation of call admission control, PSTN rerouting and Media bypass. The most popular method is to create a survivable branch appliance or survivable branch server. For medium-sized branch sites with 25-1000 users, a 'Survivable Branch Appliance' is recommended. A Survivable Branch Appliance is a third-party device that includes a server running the Lync Server 2013 Registrar, Windows Server 2008 R2, Mediation Server software, and a PSTN gateway, all in a single appliance chassis. For branch sites with 1000-5000 users, a 'Survivable Branch Server' is recommended. A Survivable Branch Server is a Windows Server-based computer that has Registrar and Mediation Server software installed on it. There are many great features of Microsoft Lync Server 2013, but it's important to provide high availability when using this program to ensure that you do cover all your bases, especially in the event of a site failure.How do your Excel skills stack up?
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