If you have 20 TB of data to backup, I would say most data deduplication appliances on the market today can handle that without too much of a problem. When you start scaling to 50 TB, 100 TB, 1 PB of backup
Some of the technologies I personally think are enterprise-ready are Dilligent Technologies and Sepaton. Both companies have had products on the market for some time now, and they are both having pretty good success in the market.
Check out the entire Data Deduplication FAQ.
This was first published in December 2007