A host device controls a storage device to perform a read operation of a read data unit with respect to selected memory areas. A read latency corresponding to the read operation of the storage device is stored in a read latency table of the host device. A determination is made whether a latency change ratio exceeds a threshold value, based on the read latency stored in the read latency table. The data host requests a data retention operation from the storage device, through a retention command, when the latency change ratio exceeds the threshold value.