SQL Server compressed backups, whether native or using a third party tool such as Litespeed, help to keep the backup sizes down - but de-dupe storage is the relatively new kid in town that saves storage, and helps those occasionally fraught relationships between DBAs and Storage Admins!
De-deuplication, or de-dupe, is where a file, or set of files, are examined for repeating segments. If the de-dupe appliance, or software, has seen the segment before then it is replaced with a reference, and the segment isn't stored again. De-dupe is particularly applicable to database backups where large amounts of data in each backup have been seen before, but it is also used in Virtalisation hypervisors where ten VMs running, say, Windows 2008 Server have the same code in memory.
Data Domain has been one of the innovating leaders of appliance de-dupe, so much so that they were acquired by EMC. Data Domain helpfully provi