This enclosure takes 2 M2 drives that plug into a usb port and can be read by your computer. It will also clone one drive to another. It said it would only clone a smaller drive to a larger one. I had two identical drives to test this. They are 500 gigabyte half full. The cloning process took 10 minutes. I then switched them and cloned them the other way which worked fine. You do not need to erase the drive the cloning process will over write it. Once cloned the drive enclosure will only report one drive. You then need to go into disc management which will report a drive letter conflict. It then gives you a method to rename one drive. This may not work on every drive pair the same size. Open both in disk management. Even drives that are listed the same size may differ by a few kilobytes. This is normal all drive have defective areas which are locked out by the hard drive and will increase over time.