Figure 2-4 shows an example of an IBM SAN Volume Controller with eight expansion  enclosures attached. The IBM SAN Volume Controller provides block-level aggregation and volume management  for attached disk storage. In simpler terms, the IBM SAN Volume Controller manages several  back-end storage controllers or locally attached disks.  It maps the physical storage within those controllers or disk arrays into logical disk images, or  volumes , that can be seen by application servers and workstations in the SAN. It logically sits  between hosts and storage arrays, presenting itself to hosts as the storage provider ( target )  and presenting itself to storage arrays as one large host ( initiator ). The SAN is zoned such that the application servers cannot “see” the back-end physical  storage. This configuration prevents any possible conflict between the IBM SAN Volume  Controller and the application servers that are trying to manage the back-end storage.  In the next topics, the terms  IBM SAN Volume Controller  and  SVC  are used to refer to both  models of the IBM SAN Volume Controller product. However, the IBM SAN Volume Controller  is based on the components that are described next. 16  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 2.2 IBM SAN Volume Controller components Figure 2-4 IBM SAN Volume Controller with expansion enclosures