Sorry. My question was incomplete, because I didn't want to mention documentation from other vendor's tools. Now, I think that It would be appropriate.
"The difference is simple, but profound. In a traditional synthetic full, the NetWorker server (or storage node) is doing all the grunt work. It’s reading all the data up into itself, combining it appropriately and writing it back down. If you’ve got a 1TB full backup and 6 incremental backups, it’s having do read all that data – 1TB or more, up from disk storage, process it, and write another ~1TB backup back down to disk. With a virtual synthetic full, the Data Domain is doing all the heavy lifting. It’s being told what it needs to do, but it’s doing the reading and processing, and doing it more efficiently than a traditional data read."
Basics – What’s a virtual synthetic full?
"That’s where NetWorker 8.1 and virtual synthetic fulls come into play. In this scenario, NetWorker instructs the Data Domain to create a new full backup via Boost. For the Data Domain, this consists of giving NetWorker back the appropriate reference data for the saveset after (mostly) jiggling pointers and updating its own back-end file data. The net result is speed. Virtual synthetic fulls are fast on Data Domain because there’s very little data being rehydrated – deduplicated data is just being adjusted."
Virtual synthetic fulls: A match made in heaven
"Virtual synthetic Backups reduce the processing overhead associated with traditional synthethic full backups."