The Full Scan – Sync schedule step performs iterates every CS object and MV object row in an MS Sync connection database (MIM, FIM, AD Connect, DirSync, etc.). It performs a hash of the object and if it differs from the record in Identity Panel it reads the full object and submits a delta.
It is important to differentiate between an initial load full scan which takes a number of hours, and a catchup full scan which simply performs a true-up of missing data and usually completes in minutes. Both operations may be down with the Full Scan step type though.
The only required parameter for a Full Scan – Sync schedule step is the Id of the MS Sync Connection environment.