An apparatus for communicating with a host system, the apparatus including a memory configured to store metadata for old data and metadata for new data, and a metadata manager configured to manage metadata, and configured to: receive new data and an overwrite request from said host system, wherein the overwrite request includes a first logical address for the old data and a second logical address, different from the first logical address, for the new data; sequentially receive from the host system a plurality, n, of overwrite requests respectively associated with partial data resulting from data splitting of the overwrite request from the host, wherein, to allow each of the n overwrite requests to be executed by an atomic operation, the metadata manager is configured to set a value of a field related to the atomic operation, and with respect to each of the n overwrite requests: acquire a physical address for the old data from the metadata using a mapping table based on the first logical address of the old data; buffer information including the physical address of the old data and information about the new data in the memory; perform an overwrite operation by writing the new data corresponding to the second logical address to a memory device and simultaneously invalidating the old data corresponding to the first logical address in response to the overwrite request; receive write completion information from the memory device; determine a value of an atomic operation end command field among the fields related to the atomic operation in the overwrite request; and based upon the determined value indicating a last one of the n overwrite requests, update metadata, including mapping information between logical addresses and physical addresses in the mapping table when the new data is written to the memory device and invalidate mapping information between the first logical address and a first physical address in the metadata, and add mapping information between the second logical address and a second physical address to the metadata, with respect to the n overwrite requests, based on buffered n pieces of new data and old data. receive new data and an overwrite request from said host system, wherein the overwrite request includes a first logical address for the old data and a second logical address, different from the first logical address, for the new data; sequentially receive from the host system a plurality, n, of overwrite requests respectively associated with partial data resulting from data splitting of the overwrite request from the host, wherein, to allow each of the n overwrite requests to be executed by an atomic operation, the metadata manager is configured to set a value of a field related to the atomic operation, and with respect to each of the n overwrite requests: acquire a physical address for the old data from the metadata using a mapping table based on the first logical address of the old data; buffer information including the physical address of the old data and information about the new data in the memory; perform an overwrite operation by writing the new data corresponding to the second logical address to a memory device and simultaneously invalidating the old data corresponding to the first logical address in response to the overwrite request; receive write completion information from the memory device; determine a value of an atomic operation end command field among the fields related to the atomic operation in the overwrite request; and based upon the determined value indicating a last one of the n overwrite requests, update metadata, including mapping information between logical addresses and physical addresses in the mapping table when the new data is written to the memory device and invalidate mapping information between the first logical address and a first physical address in the metadata, and add mapping information between the second logical address and a second physical address to the metadata, with respect to the n overwrite requests, based on buffered n pieces of new data and old data. acquire a physical address for the old data from the metadata using a mapping table based on the first logical address of the old data; buffer information including the physical address of the old data and information about the new data in the memory; perform an overwrite operation by writing the new data corresponding to the second logical address to a memory device and simultaneously invalidating the old data corresponding to the first logical address in response to the overwrite request; receive write completion information from the memory device; determine a value of an atomic operation end command field among the fields related to the atomic operation in the overwrite request; and based upon the determined value indicating a last one of the n overwrite requests, update metadata, including mapping information between logical addresses and physical addresses in the mapping table when the new data is written to the memory device and invalidate mapping information between the first logical address and a first physical address in the metadata, and add mapping information between the second logical address and a second physical address to the metadata, with respect to the n overwrite requests, based on buffered n pieces of new data and old data.