I could not find pdf solely for SAN media servers but some of the information is in the shared storage guide at
http://seer.entsupport.symantec.com/docs/290238.htm
I was looking at setting this up it in our environment year ago and did some research at that time from what i understand
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SAN media server is a media server which will backup its own data only locally on fibre (can say SAN as drives are zoned via fibre), some of the steps involved to implement,
1.install media server software on the client you want to make SAN Media server.
2. create a zone on switch, with master server, media server and tape drives
3. add the media server to the master server and update emm server on master server.
4. apply Shared Storage 0ption license on both the servers.
5. Run storage device inventory on master server and make master as robot control host.
6. test backup both on master and media.
The following blog provides some information about the SAN media server for Exchange but can be used in general.
http://juneat.blogspot.com/2010/02/setup-san-media-server-backup-exchange.html
The following kb article helps with the enteries needed for the mediserver
http://seer.entsupport.symantec.com/docs/278996.htm
Also this forum discussed the setup
http://www.backupcentral.com/phpBB2/two-way-mirrors-of-external-mailing-lists-3/symantec-netbackup-1...
Let me know if you find anything more on this and have success in backing up using the SAN Media server.