The invention relates to a storage apparatus and a method for autonomous space compaction. Embodiments of the inventive concept improve performance, energy efficiency, and capacity of storage solutions, for example, by reducing the data movement between the CPU and the storage device and increasing the available capacity of the underlying storage devices via in-storage support for data compaction. Embodiments include a storage apparatus and method for autonomous in-storage space compaction initiated by a host-side command and according to metadata specified by a host. A space compact engine can function as an independent module or logic section within a storage device, which can migrate data within the storage device, thereby freeing up capacity and making preexisting data more compact. The space compact engine can cause self compact operations, self compact and trim operations, move and compact operations, and/or merge and compact operations. The space compact engine can notify the host of the completion of the operations.