Netapp deduplication - is a new technology to control the rate of data growth. The average UNIX or Windows disk volume contains thousands or even millions of duplicate data objects. As data is created, distributed, backed up, and archived, duplicate data objects are stored unabated across all storage tiers. The end result is inefficient utilization of data storage resources. By eliminating redundant data objects and referencing just the original object, huge benefit is obtained through storage space efficiencies - which results in "Cost benefit" and "Management benefit".
Deduplication implementation guide : http://media.netapp.com/documents/tr-3505.pdf
Deduplication estimation calculator : http://www.dedupecalc.com/