SAN is the acronym for Storage Area Networks.  These are high-performance, high-availability storage networks with the ability to cross great distances using fibre channel components and fiber optic interfaces.  SANs are accessible by multiple host computers. 

While attractive, they also have drawbacks:  SANs operate on a block-level, while hard drives work with file names.  At some point between the SAN and the workstation, a block-level to file-level conversion must take place.  Typically this burden falls on the file servers, ensuring them sole access to the SAN, limiting the client to file server access. 

It appears that NAS devices provide the most open, vendor-neutral solutions for a SAN can be just as effective as a NAS, it all depends on how well the software is capable of doing its job retrieving and archiving the image data.