You will only need 2 vscan servers for redundancy. These can easily be VMWare instances.
Virus scanning is much more efficient this way than they way it has to be done on windows. Read the TR. 'vscan' functionality doesn't scan the entire filesystem like you have to do on Windows. It just makes sure that new writes are scanned and that reads are scanned if the vscan server has newer virus definition files.
You will be able to manage 10's of TB with just 2 vscan servers. You'll never get close to that using windows servers for file server, not to mention the extra server/power/heat load of having to dig through everything once a week.
The only really challenge is learning to tune your vscan software.
Basically we have a Filer configured with Clustered ONTAP 8.2 and trying to use McAfee Scanning solution, the McAfee side is configured with connector installed and ONTAP Management LIFs for polling configured but strugling with NetApp side of things. We have followed the guide but keep getting error -
10/31/2014 10:46:12:709 3224 Error SCAN RESULT - : File to scan ="\\?\UNC\10.19.11.133\ontap_admin$\restore_test\StorageCapacityIssues.pptx result is Error the file is locked and could not be scanned. Status Code 222200020