Data deduplication changes all the rules in secondary storage. Most notably, it belies the rules that say every gigabyte of primary storage is represented by 10GB of backups, and the canard that tape is cheaper than disk.

There's been a flurry of debate about deduplication--both for and against--that has generated confusion, fear, uncertainty, doubt and misconceptions about the technology. Simply put, deduplication technologies identify and eliminate redundant data, significantly reducing the amount of disk needed to store the deduped data. Though various deduplication systems eliminate redundant data differently, all of the approaches look at the data on a subfile (block) level to determine if the system has seen the data before. If it hasn't, it stores it. If it has seen the data before, it ensures that it's stored only once and all other references to that data will just be pointers.