Operating side, nothing really revolutionary. You just have to connect the adapter to the power of the house (the power supply is provided UK!) And connect the device to the Thunderbolt port on your Mac (tested here with a MacBook Pro 2011 - 13 inches - OS Lion) with a Thunderbolt cable, kindly supplied by Western Digital for the purposes of this test, but usually not provided (count 50 still this official cable).
When first starting, it is proposed to install a small software that helps manage 2 hard drives, to prevent possible failures - either in hardware (eg overheating) or computer - or format hard drives. And it is here that reveals the true value of this case: it is possible either simply using 2 separate hard drives (JBOD - as if they were two 2 terabyte hard drives); either to use one partition for the 2 discs (in this case the computer considers this a 4 terabyte hard drive!) (RAID 0); or whether to use the 2 hard drives to backup your data 2 times (1 each!) for safety (RAID 1).
We must emphasize the value of the first solution that allows the use of a disc recording format of the Mac and on the other drive Windows size (provided of course that Windows is installed on a Mac, Thunderbolt requires).
Recently, Apple offers the Time Machine application. This application provides a copy of all your computer (in one click), updated regularly (several times a day, by default) at the option of deletions / Data creations. The great interest is the possibility to go back at any time (without saving each time the entire computer!).
The housing offers this application at the first startup. If the application already has a hard drive of reference, simply go into TimeMachine and click "select disk".
I personally use TimeMachine with the housing in safety mode (1 copy on each disk). During the first backup, the system has copied 280 giga (x2!) In just over 3 hours (I used the Mac at the same time to do other things).
Hardware side, the housing does not heat at all, even after intensive use, and it makes no noise. A small LED on the front lets you know if it is on, off, or in sleep. It should also be noted that there is no switch over. To turn it off, cut the power supply (after removing it properly on the Mac obviously).
A guide "paper" quick start is provided, and a more detailed digital guide (thirty pages, multi-languages including French).