A data storage device may include a memory device including a plurality of memory blocks having a plurality of free memory blocks and a controller configured to control an operation of the memory device, wherein the controller performs a block allocation operation of allocating one or more free memory blocks among the plurality of free memory blocks as one or more programmable memory blocks, and performs a garbage collection (GC) error defense operation of checking whether a GC operation for the plurality of memory blocks has performed successfully, in response to the block allocation operation.