text: *File/record/namespace virtualization*and*File/record subsystem*layers translate records or 
  files that are required by applications to vectors of blocks, which are the language of the*Block*
  *Virtualization*layer.*Block Virtualization*layer, in turn, maps requests of the higher layers to 
  physical storage blocks, which are provided by*Storage devices*in the*Block subsystem*. 
  
  Each of the layers in the storage domain abstracts away complexities of the lower layers and 
  hides them behind an easy-to-use, standard interface that is presented to upper layers. The 
  resultant decoupling of logical storage space representation and its characteristics that are 
  visible to servers (storage consumers) from underlying complexities and intricacies of storage 
  devices is a key concept of storage virtualization. 
  
  The focus of this publication is*block-level virtualization*at the*block virtualization layer*, 
  which is implemented by IBM as IBM Spectrum Virtualize software that is running on IBM 
  SAN Volume Controller and the IBM Storwize family. The IBM SAN Volume Controller is 
  implemented as a clustered appliance in the storage network layer. The IBM Storwize family 
  is deployed as modular storage that can virtualize its internally and externally attached 
  storage. 