An operation method of a storage device which includes a nonvolatile memory device, the method comprising: 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, wherein the first KV command and the second KV command are KV commands of a same type; wherein the second value includes information about an administrative command and a command identifier corresponding to the first administrative operation, wherein the transmitting of the first value corresponding to the first key from the nonvolatile memory device to the external host device as the first user data, in response to the first KV command, includes: determining a first location of the first value corresponding to the first key, based on a key index including information about a plurality of keys and locations of values respectively corresponding to the plurality of keys; reading the first value from the nonvolatile memory device, based on the determined first location; and transmitting the read first value to the external host device as the first user data, wherein the performing of the first administrative operation based on the second value corresponding to the second key, in response to the second KV command, includes: determining a second location of the second value corresponding to the second key, based on the key index; reading the second value, based on the determined second location; and performing the first administrative operation, in response to the read second value, wherein the second value is included in an internal key-value pair stored in a memory device of the storage device. 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, wherein the first KV command and the second KV command are KV commands of a same type; wherein the second value includes information about an administrative command and a command identifier corresponding to the first administrative operation, wherein the transmitting of the first value corresponding to the first key from the nonvolatile memory device to the external host device as the first user data, in response to the first KV command, includes: determining a first location of the first value corresponding to the first key, based on a key index including information about a plurality of keys and locations of values respectively corresponding to the plurality of keys; reading the first value from the nonvolatile memory device, based on the determined first location; and transmitting the read first value to the external host device as the first user data, wherein the performing of the first administrative operation based on the second value corresponding to the second key, in response to the second KV command, includes: determining a second location of the second value corresponding to the second key, based on the key index; reading the second value, based on the determined second location; and performing the first administrative operation, in response to the read second value, wherein the second value is included in an internal key-value pair stored in a memory device of the storage device. determining a first location of the first value corresponding to the first key, based on a key index including information about a plurality of keys and locations of values respectively corresponding to the plurality of keys; reading the first value from the nonvolatile memory device, based on the determined first location; and transmitting the read first value to the external host device as the first user data, wherein the performing of the first administrative operation based on the second value corresponding to the second key, in response to the second KV command, includes: determining a second location of the second value corresponding to the second key, based on the key index; reading the second value, based on the determined second location; and performing the first administrative operation, in response to the read second value, wherein the second value is included in an internal key-value pair stored in a memory device of the storage device. determining a second location of the second value corresponding to the second key, based on the key index; reading the second value, based on the determined second location; and performing the first administrative operation, in response to the read second value, wherein the second value is included in an internal key-value pair stored in a memory device of the storage device.