Source deduplication is a process through which duplicate data is removed from a source device. It is used in data backup procedures and provides better backup storage utilization and better data transfer rates on low bandwidth systems. Source deduplication is achieved through a purpose-built software or hardware appliance.
Techopedia explains Source Deduplication
Source deduplication is primarily a data deduplication technique. It works when the data at the source device is reviewed for duplicates. This is done when the source deduplication enabled client device connects with the remote backup server to view the list of files already updated. If a file or data block is already present on the source device, it is considered a duplicate and is removed from the backup data queue. If the source has a newer version of the file than the target device, only changes are updated and backed up on the target.
Source deduplication is considered slower than target deduplication because it creates additional workload for the client device; however, the actual rate of data transfer is better because it removes duplicates before backup transmission.