High Availability (HA) and Disaster Recovery (DR) capabilities continue to improve in Skype for Business Server 2015 to provide even greater uptime reliability and performance for end users. Fundamentally the Front-End HA/DR capabilities are built upon the Windows Fabric v1 foundation that was introduced in Lync Server 2013, and now improved with v3 in Skype4B server, For the Back-End servers the redundancy is built on SQL Mirroring or Always-On technologies This article aims to provide some of the best practices for Front End Server HA+DA in Skype4B server. For readers already familiar with these concepts, then this article can also serve as a refresher and/or reference.
HA in the Skype4B Front-End pool is the ability of the server pool to continue servicing users in the event of a failure of 1 or more servers within the pool. Front-End pool HA is based on clustering via HLB and DNS load balancing built into the servers to automatically distribute groups of users across the various front end servers in a pool. During startup, 85% of all servers in the pool must be started in order for the entire pool to be functional. This is known as achieving Routing Group level Quorum. After the pool is operational, then only 50% of the servers in the pool must be running in order for the pool to remain functional. This is called achieving Pool Level Quorum and is not to be confused with Routing Group Level Quorum. The table below shows the numbers for these two quorum types: