3000850 is a recommended rollup for failover clusters. beside few others a lot of fixes around Hyper-V and Clustering are included.
A cumulative update that includes the security updates and nonsecurity updates including Failover Clustering updates that were released between April 2014 and November 2014. Available from Windows Update and for individual download from Download Center. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
Checkout the details here