Make a clone of your hard drive is also a way of backing up data. As once the original hard drive has some problems, as it stops spinning, or have serious bad sectors, you can recover most data from the cloned disk. If you take cloning as a way to backup your data, you need to clone the units very often and need a cloning tool much easier to do that for you.
Here comes the double Rack USB / eSATA HDD Dock that also functions as a hard disk cloning tool. The dock has two slots, which you can connect 2 hard disks in the two slots and have a drive to be cloned to another. This hard drive dock is very useful for those who often have to clone their hard drives.