An operation method of a storage device, which includes a nonvolatile memory device, includes receiving a first key-value (KV) command including a first key from an external host device; transmitting a first value corresponding to the first key from the nonvolatile memory device to the external host device as first user data, in response to the first KV command; receiving a second KV command including a second key, from the external host device; and performing a first administrative operation based on a second value corresponding to the second key, in response to the second KV command. The first KV command and the second KV command are KV commands of a same type.