According to one embodiment, a storage device is accessible by an external device via an interface and includes a nonvolatile memory including one or more blocks, and a controller electrically connected to the nonvolatile memory. The controller receives from the external device a request and a notification indicating that a response performance of the request is to be lowered. In response to receiving the request and notification, the controller determines a response time longer than a processing time of the request, and executes a first performance lowering process that executes a block managing process of the nonvolatile memory by using an idle time which is a difference between the response time and the processing time of the request or executes a second performance lowering process that lowers the response performance so as to process the request by spending the response time.