Microsoft Scale-Out File Server definition

Microsoft Scale-Out File Server is an active-active clustered storage feature based on Server Message Block (SMB) 3.0 to provide continuous availability of file shares in Windows Server. 

Scale-Out File Server was introduced in Windows Server 2012 and is designed for use as a file share for server application data, such as Microsoft Hyper-V virtual machines (VMs) and SQL Server. The file shares are available at the same time on all nodes in the cluster. The active-active feature keeps data on the file share available despite downtime on a node either for maintenance or from a failure.

Scale-Out File Server uses the total bandwidth of the cluster nodes to deliver data. Administrators can boost bandwidth by adding more nodes to the cluster. Scale-Out File Server optimizes traffic by providing automatic rebalancing of connections to provide the fastest route to the file share.

 Courtesy: Margaret Rouse