A method of managing a garbage collection (GC) operation includes: comprising: selecting a source block and at least one candidate source block from the flash memory; calculating an overall valid page percentage according to a number of valid pages in the source block and the at least one candidate source block; determining a GC-to-host base ratio according to the overall valid page percentage; and performing the GC operation on the source block according to at least the GC-to-host base ratio.