A storage device includes NVM package and a controller connected to the NVM package through a channel and controlling operation of the NVM package. The NVM package includes an interface chip, first NVM devices connected to the interface chip through a first internal channel and second NVM devices connected to the interface chip through a second internal channel. The interface chip selects the first internal channel in response to an operation request received from the controller and connects the first internal channel to the channel. The interface chip also determines whether retraining is necessary in relation to the second internal channel and transmits a retraining request to the controller when retraining is necessary.