What Symantec is actually recommending now is to use a traditional Unix or Windows client and NFS-mount or CIFS-mount the data. Then do your normal backups to a PureDisk storage unit and do continuous incrementals and synthetic fulls. With the new PD code, a synthetic full only does pointer changes so they got like a bat out of...
As an extra bonus, because you're using a non-NDMP client, you can restore the file to anywhere, not just the same NDMP type of host that you started from.
As a double-added bonus, a Unix or Windows license (list $2,595 to $6,095 for x86/x64 clients) is a LOT cheaper than an NDMP license, especially if you a have big filer (list $3,500 to $15,500).
The de-dupe option is VERY pricey though at $5k per front-end TB (MSRP). In our environment, we're about 180TB of used space at the moment. The list price of backup it all up with de-dupe would top a million bucks with the media servers and the de-dupe licenses. And that doesn't include the disk to put it to.
.../Ed