content_image/982121.jpg
Figure 2-4 shows an example of an IBM SAN Volume Controller with eight expansion enclosures attached. 

## 2.2 IBM SAN Volume Controller components 

<img src='content_image/982121.jpg'>

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. 

