Actually, it does. There are lots of types, and they store data differently. See, for example, this description. Regardless of the method used, the software will have a method for re-assembling the pieces. Alan, this disagreement is irrelevant to your question. If you want to be able to access the copies without using a restore function, a mirror (copy) is your answer. But if your only concern is being able to retrieve the file by some method, either will work. The file manager I used for my mirror, Directory Opus, makes this extremely simple. I have it configured so the active window comprises three panels: one on the left that shows the directory tree, and then two larger panels that show specific parts of the structure, both directories and files. I have all of the photos in my active catalog under one parent directories named "photos". So I just set the middle and left panel to the same part of \photos on the different drives, and drag from the copy to the mail disk. Trivially easy. It also allows you to compare file dates.