A storage device includes a non-volatile memory including a plurality of non-volatile memory cells, a buffer memory configured to temporarily store write data to be written to the non-volatile memory or read data read from the non-volatile memory, and a controller configured to receive a sleep mode signal from an external host. When the sleep mode signal is received by the controller, the controller is configured to block a first power supplied to the non-volatile memory and set the buffer memory to one of a first mode in which a second power is blocked from being supplied to the buffer memory and a second mode in which the buffer memory operates with low power. The write data stored in the buffer memory is written to the non-volatile memory when the buffer memory is set to the first mode.