1. A method for use in a dispersed storage network (DSN) including a dispersed storage (DS) processing unit and a plurality of storage unit sets, the method comprising: receiving, by a first storage unit set and a second storage unit set, a plurality of sets of encoded data slices generated by the DS processing unit for storage, the plurality of sets of encoded data slices including dispersal-encoded portions of one or more data objects, wherein the first and second storage unit sets are utilized to mirror storage of the one or more data objects; identifying, by storage units of the first storage unit set, stored encoded data slices that are unsynchronized with the second storage unit set as unsynchronized data slices; generating, by the storage units of the first storage unit set, a record identifying the unsynchronized data slices; detecting, by the storage units of the first storage unit set, availability of at least one storage unit of the second storage unit set; in response to the detecting, facilitating, by the storage units of the first storage unit set, copying of particular unsynchronized data slices to corresponding storage units of the second storage unit set; and in response to completion of the copying, updating the record, by the storage units of the first storage unit set, to indicate that the particular unsynchronized data slices have been synchronized.