1.1 Storage virtualization terminology 2  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 Storage virtualization  is a term that is used extensively throughout the storage industry. It can  be applied to various technologies and underlying capabilities. In reality, most storage devices  technically can claim to be virtualized in one form or another. Therefore, this chapter starts by  defining the concept of storage virtualization as it is used in this book. IBM describes storage virtualization in the following way: Storage virtualization is also defined in the Storage Networking Industry Association’s (SNIA)  shared storage model version 2, shown in Figure 1-1.  The model consists of the following layers: Applications typically read and write data as vectors of bytes or records. Alternatively, storage  presents data as vectors of blocks of a constant size (512 bytes or, in newer devices, 4096  bytes per block). The  File/record/namespace virtualization  and  File/record subsystem  layers  convert records or files required by applications to vectors of blocks, which are the language  of the  Block Virtualization  layer. The  Block Virtualization  layer in turn maps requests of the  higher layers to physical storage blocks, provided by  Storage devices  in the  Block subsystem . 1 Source: Storage Networking Industry Association. GLYPH<SM590000> Storage virtualization is a technology that makes one set of resources resemble another  set of resources, preferably with more desirable characteristics. GLYPH<SM590000> It is a logical representation of resources that is not constrained by physical limitations and  hides part of the complexity of those resources. It also adds or integrates new functions  with existing services, and can be nested or applied to multiple layers of a system. GLYPH<SM590000> Application : the user of the storage domain GLYPH<SM590000> Storage domain , which is split into: – File/record/namespace virtualization  and  File/record subsystem – Block Virtualization – Block subsystem