How do I defragment a removable hard disk?

Mobile hard disk with the increase in time, there will be a lot of disk fragmentation, the removal of debris from the hard drive can not be free to clean up.

　　How do I defragment a removable hard disk?

First copy all the data in the mobile hard disk for backup, and then copy back after finishing. Because the external hard drive through a USB interface and host connection, if there is data uplink downlink, it will lead to a decrease in speed. In the collation, the data will frequently uplink downward, if the speed is slow, the process will be very long, so it is better to copy out and then copy back.