Greg Schulz has a great post on his StorageIO blog about VMware VVOL’s.

With a normal SCSI LUN the underlying storage system has no knowledge of how the upper level operating system, hypervisor, file system or application such as a database (doing raw IO) is allocating the pages or blocks of memory aka storage. It is up to the upper level storage and data management tools to map from objects and files to the corresponding extents, pages and logical block address (LBA) understood by the storage system. In the case of a NAS solution, there is a layer of abstractions placed over the underlying block storage handling file management and the associated file to LBA mapping activity.

Reading and  gathering  knowledge  of VMware VVOL’s will be needed much more    in the coming days, so do yourself a favor and read the post.

http://storageioblog.com/vmware-vvols-and-storage-io-fundementals/