Server 2008 R2 / 2012 came with a new failover Cluster feature called Cluster Shared Volumes (abbrev: CSV). This is a new feature that enables accessing a LUN from multiple a Windows Failover Cluster Nodes at the same time. In past, this was not possible on Windows Failover Clusters.
Lets take a look on to the details.
- all nodes in a cluster can access the LUN at the same time, no failover needed
- if a node’s storage connection fails / has issues, the node can send the write/read requests over LAN to another Node to write/read the needed stuff for him (“The cluster will re-route the communication through an intact part of the SAN or network”, Technet  )
- From Technet: “Be sure to review carefully what your backup application backs up. Also, for management operating-system based backup, ask your backup application vendor about the compatibility of your backup application with Hyper-V and with Cluster Shared Volumes.” 
- a MUST for Hyper-V, but no advantage for Applications that don’t run more than one instance on the same volume at the same time (e.g. SQL failover cluster, one instance, two servers)
- NOT SUPPORTED for SQL Server clustered Workloads 
 Understanding Cluster Shared Volumes in a Failover Cluster
 Recommendations for Using Cluster Shared Volumes in a Failover Cluster
 Backing Up Cluster Shared Volumes
 Use Cluster Shared Volumes in a Windows Server 2012 Failover Cluster