Q. How can I make direct-attached storage highly available from multiple nodes with Windows Server 2012 R2?
A. In Windows Server 2012 R2 there is no "virtual SAN"-type feature that enables direct-attached disks that are local to a specific host to be joined together logically with direct-attached disks in other nodes in a cluster. The desired functionality would be for resiliency to be provided by replicating the data across nodes, and then exposing the aggregated storage to clients using a protocol such as SMB or iSCSI. This type of feature is expected in the next version of Windows Server, which in preview has synchronous block-level replication.
In Windows Server 2012 R2 some kind of shared storage is required. This could be a SAN or an external storage enclosure that is then directly attached to two or more nodes. If using the external storage enclosure approach, the disks in the external storage enclosure could be placed in a clustered storage space and then used simultaneously by the nodes in the cluster. It would then be possible to expose that shared storage to other machines via SMB or iSCSI using Windows as the file server.
DFS-R is not a solution to replicate storage between nodes for most workloads, as it replicates only closed files. This means it would not be able to replicate, for example, a VHDX file that was being used as the storage for a Windows Server iSCSI target.