How have the options for VM storage changed with Hyper-V 3.0?
In Hyper-V versions prior to 3.0, the options for virtual machine storage are somewhat limited. If a Hyper-V server is not a part of a cluster, virtual machines usually reside on direct-attached storage (although SAN storage is supported). This could be anything from an internal storage array to individual physical hard disks.
Before the release of Hyper-V 3.0, clustered Hyper-V servers were required to use shared storage. Shared storage involves connecting individual cluster nodes to a Cluster Shared Volume through either iSCSI or Fibre Channel. Naturally, this type of storage is expensive and is typically beyond the financial reach of smaller organizations.
Microsoft has designed Hyper-V 3.0 to be much more flexible in terms of the types of storage that are supported. Even though Cluster Shared Volumes are still the preferred type of storage for Hyper-V, in Version 3.0 they are far from being the only option.
One of the new storage options involves storing virtual machines on file servers. This allows a virtual machine to make use of centrally accessible storage without requiring the organization to build a dedicated Cluster Shared Volume.
Of course, not just any file server is suitable for virtual machine storage. In fact, Microsoft requires the file server to use the SMB version 2.2 protocol, which is more robust than prior versions -- with enough extra bandwidth and resiliency against network failures that, with the upgraded protocol, Microsoft will support storing virtual machines on file servers. (The extra bandwidth comes from SMB 2.2's multichannel nature; if multiple paths exist between a source and a destination, the protocol can utilize those paths to increase the overall bandwidth.)