Everything depends of your needs, for small size environment (1-10 Media Servers) you can use the Netbackup Deduplication or MSDP option, trick is to make the clients to run the deduplication if you put all the dedup load in the MSDP boxes they will underperform thats why this solution is not good for big environments.
For Medium Size Environment (11-30 Media Servers) you can use the Netbackup Appliances mixed with some MSDP will depend of budget here is the same tricket you let the 75% of the deduplication to run on the client side because if you let more than 40% of the dedup to run on any of the appliances or an MSDP box they will underperform and you will be force to add more devices, like I said it depends of budget
For Large Size Environment (31-60 Media Servers) DataDomain is the best option here you dont need to care of client deduplicating data this machines rule the deduping world, just to make a difference I have see 1 of this Devices to Backup 40TB in one night without a single complaint and duplicate the 40TB during the day without a problem (Using a VTL configuration which is worst setup for DD's) this is a 1200MB/sec throughput compared with MSDP or the NBU Appliances the most they will give you is around 140MB/sec, why becuause the Netbackup Deduplication is design to put most of the load on the client side which is a good idea because you distribute the load and for those clients that you cannot afford to do this you let the MSDP or Appliance do the deduping. Keep in my that if you add a DDBoost config in the DataDomains your speeds easily can up up to 3000MB/sec.
In Conclusion, if you are small get an MSDP solution is included in the Netbackup 7 license and plan well your storage if you have something big, go with the big guys.
Hope this helps.
Best Regards.
