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Source deduplication is the removal of redundancies from data before transmission to the backup target.
Source deduplication products offer a number of benefits, including reduced bandwidth and storage usage. No additional hardware is required to back up to a remote site and many source deduplication products also support automation for offsite copies. On the other hand, the source-based method can be slower than target deduplication, especially for large (multiple terabyte) amounts of data. Because of the increased workload on servers, overall backup times may increase
Source deduplication works through client software that communicates with the backup server to compare new blocks of data with previously stored blocks of data. If the server has previously stored a block of data, the software does not send that block and instead notes that there is a copy of that block of data at that client. If a previous version of a file has already been backed up, the software will compare files and back up any parts of the file it hasn't seen. Source deduplication is well suited for backing up smaller remote backup sets.