Single-Instance Storage (SIS)
Comparison to deduplication
If you change the title of a two-megabyte Microsoft Word document, SIS retains the first copy of the Word document and stores the entire copy of the modified document. Any change to a file requires that the entire changed file be stored again. Data deduplication, which reduces subfile-level data, recognizes that only the title had changed and so only stores the new title, with pointers to the rest of the document's content segments.
Generally, EMC Data Domain systems enable two to four times data reduction on an initial full backup, six to seven times reduction on subsequent file-level incrementals, and 50 to 60 times reduction on subsequent full backups. SIS doesn't offer benefits to the initial full or to file-level incrementals so, at that level, EMC Data Domain deduplication is 80 to 90 percent more efficient—meaning that much less storage is required—than SIS.
It's an even bigger gap with structured data. Databases change daily and are generally backed up in full daily. SIS offers no benefit here, but Data Domain systems can reduce backup storage requirements by 10 to 30 times with this data.