Check this thread

http://www.symantec.com/connect/forums/symantec-endpoint-protection-netbackup-7103

The recommended software for scanning the NAS Storages would be the Symantec SCan Engine for NAS:

http://www.symantec.com/protection-engine-network-attached-storage

It is software specifically designed for that purpose:

Symantec Protection Engine for Network Attached Storage provides scalable, high-performance threat detection services. These services protect valuable data stored on network attached storage (NAS) devices, providing increased scanning performance and improved detection capabilities for protection against multi-blended threats. Protection Engine includes Symantec's industry-leading malware protection for fast, scalable, and reliable content scanning services. These help organizations protect their data and storage systems against the ever-growing malware threat landscape. Malware definitions and engines are updated automatically with no interruption in malware scanning using Symantec LiveUpdate. Definitions can also be distributed centrally to multiple deployments utilizing the included Symantec LiveUpdate Administrator application.

Thread about the differences:

https://www-secure.symantec.com/connect/forums/dif...

Hello,

For many reasons, including the typical large (terabytes) capacity of NAS, the Symantec Scan Engine is the right product to secure these machines.

The use of the Symantec AntiVirus or Symantec Endpoint client to scan drives on a NAS device is not recommended and is not supported.

I would recommend - Symantec Protection Engine for Network Attached Storage

Symantec Protection Engine for Network Attached Storage provides scalable, high-performance threat detection services. These services protect valuable data stored on network attached storage (NAS) devices, providing increased scanning performance and improved detection capabilities for protection against multi-blended threats. Protection Engine includes Symantec's industry-leading malware protection for fast, scalable, and reliable content scanning services. These help organizations protect their data and storage systems against the ever-growing malware threat landscape. Malware definitions and engines are updated automatically with no interruption in malware scanning using Symantec LiveUpdate. Definitions can also be distributed centrally to multiple deployments utilizing the included Symantec LiveUpdate Administrator application.

Check this Thread:

different between Symantec Endpoint protection and Symantec Scan Engine

https://www-secure.symantec.com/connect/forums/dif...

https://www-secure.symantec.com/connect/forums/symantec-endpoint-client-symantec-av-nas-supported

Hope that helps!!