Disclosed is a method of operating a storage controller which communicates with a non-volatile memory device. The method includes outputting a first command including a request for on-chip valley search (OVS) count data of a memory region of the non-volatile memory device to the non-volatile memory device, wherein the OVS count data includes a first count value and a second count value of a first read voltage and a third count value and a fourth count value of a second read voltage, receiving the OVS count data from the non-volatile memory device, determining a distribution type of the memory region to be a predicted distribution type, from among a plurality of distribution types, based on the OVS count data, and determining a subsequent operation, based on the predicted distribution type.