Windows 2012 R2 Cluster: Disk können nicht Online gebracht werden

There are few possible ways to go:

1) Use application built-in clustering features (like some iSCSI SAN & NAS software has out-of-box and also MS SQL Server can do database mirroring doing what you want with DAS etc). That's PREFERRED way to go as it's true HA and usually comes for free or very cheap.

2) Use third-party software solution taking DAS and converting it to fault-tolerant HA SAN. Like this solution:

http://hyperv.starwindsoftware.com/two-node-configuration-for-hyper-v-using-starwind-iscsi-san

There's a free version with limited capacity as well. Also you may Google to find competitors, some of them are also native Windows (no guest

VM overhead) and some are pure VSA (for this you need Hyper-V role enabled on both Windows hosts and also be prepared for performance

degradation and long syncs after reboots).

3) If you can allow some downtime and data loss (RTO/RTPs are not that strict) and you also have Hyper-V role enabled and you run Windows Server 2012 you may try Hyper-V replica (~5 minutes lag and data loss, no automatic failover because of a possibe brain split issue, compression only in WAN channel but comes for free). DFS does not play well for frequently changed huge database files unfortunately :(