A method for compressing data by storing only changes to the original data. For example, when a document is created, it is stored as a regular, complete file. When changes are made, deduplication stores only the data that has been modified in a subsequent file with indexes to the original. The changes may be identified by bytes or blocks.|
In file deduplication, only one copy of the file is stored even though it may be referenced from many sources. For example, if the same attachment is used in several e-mail messages, the second and subsequent messages are changed to link to the original attachment rather than duplicating it each time.