A method begins by processing modules in a dispersed storage network (DSN) identifying a memory device having a legacy slice storage format (SSF) to a second SSF and that includes a first encoded data slice (EDS) of a set of EDSs. When at least a predetermined threshold number of EDSs of the set of EDSs are included within one or storage units (SUs) excluding the first EDS the method continues by transitioning the first SSF of the memory device to the second SSF, and performing a rebuilding process using the at least the decode threshold number of EDSs of the set of EDSs to generate a rebuilt first EDS. The method continues by storing the rebuilt first EDS within the memory device to replace the first EDS that was deleted during the transitioning.