A method begins with storage units receiving a request to transfer a copy of a set of encoded data slices from two or more source virtual storage vaults to a destination virtual storage vault. The method continues with each storage unit obtaining a slice transfer map and determining whether the storage unit supports one of the two or more source virtual storage vaults. For each supporting storage unit, the method continues with each supporting storage unit determining, based on the slice transfer map, a sub-set of encoded data slices of the set of encoded data slices that is stored within the one of the two or more source virtual storage vaults by the supporting storage unit. The method continues with the supporting storage unit sending the sub-set of encoded data slices to a corresponding storage unit that is supporting the destination virtual storage vault.