1. A data storage system comprising: non-volatile memory (NVM) configured to store data in a plurality of memory data units, a memory data unit corresponding to a unit of storage in the NVM, wherein at least some memory data units have a different format; and a controller configured to: retrieve from the NVM data stored in a first memory data unit, the first memory data unit further storing metadata associated with the data, wherein the data is encrypted and the metadata is not encrypted, and using the metadata and without decrypting the data, migrate the data from the first memory data unit to a second memory data unit, the format of the second memory data unit being different than the format of the first memory data unit, wherein migrating the data from the first memory data unit to the second memory data unit causes at least some data stored in the first memory data unit to become invalid, and wherein migrating the data from the first memory data unit to the second memory data unit causes improved performance or reliability of the data storage system, wherein the NVM comprises a non-volatile solid-state memory array and a magnetic storage, wherein a physical storage unit of the non-volatile solid-state memory array is larger in size than a physical storage unit of the magnetic storage, and wherein the controller is further configured to format the data to be stored in a physical storage unit of a different size in performing the migration.