1. A method comprises: determining data to migrate, wherein the data is encoded and stored as a plurality of sets of encoded data slices in a first set of dispersed storage (DS) units, wherein the data was encoded by: dividing the data into data segments; for each data segment, dispersed storage error encoding a data segment in accordance with first error coding dispersal storage function parameters to produce a set of the plurality of sets of encoded data slices, wherein the set of encoded data slices includes a first number of encoded data slices and wherein at least a first decode threshold number of the first number of encoded data slices are needed to recover the data segment; retrieving at least a read threshold number of encoded data slices for each set of the plurality of sets of encoded data slices, wherein the read threshold number is less than a total number of encoded data slices in a set of encoded data slices of the plurality of sets of encoded data slices; dispersed storage error decoding the at least the read threshold number of encoded data slices for each set of the plurality of sets of encoded data slices in accordance with the first error coding dispersal storage function parameters to reproduce the data; dispersed storage error encoding the reproduced data in accordance with second error coding dispersal storage function parameters to produce a plurality of sets of second encoded data slices, wherein a set of the plurality of sets of second encoded data slices includes a second number of encoded data slices and wherein at least a second decode threshold number of the second number of encoded data slices are needed to recover a corresponding data segment; and for each set of the plurality of sets of second encoded data slices, sending at least a write threshold number of second encoded data slices to a second set of DS units for storage therein: wherein the write threshold number is less than the total number of encoded data slices in the set of encoded data slices and is greater than the read threshold number.