image from http://www.kintec.cn/
dd can copy one entire drive to another.
!! Note that this process will overwrite everything on your destination drive, so check to make sure there is nothing on your USB drive that you wanted to keep.
To do that, know first your available hdd.
1. Check Available HDD
$ diskutil list
if you see the output like this:
2. Unmount the target disk by
$ diskutil unmountDisk /dev/disk2
I want to clone hdd from Andy to Toshiba
3. DD Command
dd if=/dev/disk1 of=/dev/disk2 bs=32M
if= is simply telling the program what the input is
/dev/disk1 is your source hdd
of= is telling the program what the output target
/dev/disk2 is the target hdd.