Single Instance Storage (SIS) / Deduplication is a becoming a significant issue/marketing point, due to the explosion of data storage/capacity requirements.

This is especially true as the adoption of server (and coming/now desktops) virtualization is now growing into middle/lower-middle tier businesses. If you have 20 virtualized Win2008 servers. Do you really need to use 20 times the disk space to store 20 copies of the same Windows EXEs/DLLs?

A number of SAN solutions offer this feature including; MS Storage Server, Falconstor/Nexxan, NetApp and EMC.