To add a follow-up on dedupe technologies, there is generally two schools of thought. Inline dedupe and post process dedupe. Each has advantages and disadvantages, though each vendor that implements has a way to spin that, or technology to minimize their limitations..
Post process vendors (Exagrid as an example) require MORE disk to stage your backup set, then will later dedupe it to another volume internal to that appliance. Ingests are usually higher this way, and sized properly you can restore out of the staging area so restores could be faster. The downside is that you'll use more rack space, more power, and more cooling.
Inline dedupe (DataDomain and now Quantum) can dedupe data in real-time as it's fed to the appliance. The CPU is usually a quadcore or better, with lots of RAM. Since the ingest is not as fast as a "post-process," vendor that is just backing up to disk first; DataDomain has come up with BOOST which helps offload some of the dedupe to the backup server. This slightly offsets the performance hit and brings the ingest speeds on par with post-process vendors.
YMMV, each have pros and cons, levels of complexity, costs, etc. Others may integrate with your bakup app via OST in BackupExec, or even offer better dedupe rates based on their maturity in the market. So test each vendor, don't ever settle on price alone.
