A storage device performs a read operation by restoring an ON cell count (OCC) from a power loss protection (PLP) area of a nonvolatile memory. The nonvolatile memory includes a memory blocks, a buffer memory and a controller. The buffer memory stores a first ON cell count (OCC1) indicating a number of memory cells turned ON by a first read voltage and a second ON cell count (OCC2) indicating a number of memory cells turned ON by a second read voltage among the memory cells connected to a reference word line. The controller stores the OCC1 for each of the memory blocks in the PLP area when a sudden power off occurs in the storage device.