Archiving files to a hard drive

I am interested in the Western Digital My Book Essential 2
TB USB 3.0 Desktop External Hard Drive. 
I have read that the software included in this drive, WD Smartware, will back up my computer automatically.  However, if I delete a file on my computer
will that file also be deleted on the external hard drive? I want something that
will archive files.

My computer has only 300 GB and it has
filled up.  I have archived some of those
files to a Seagate 2 TB drive.  It would
be good to have the WD drive automatically update and hold all files and then I
would back up the WD drive to the Seagate drive so I have two copies of all
files.  Is that what you drive does or
will it delete files that are no longer on my computer?

Maybe I did not explain myselfwell.  I basicaly want to know if the WD software will “mirror” my computer and delete files on the external hard drive that I delete on the computer.  I don’t want it to delete them becuse I want to archive on to the bigger external hard drive since my computer is running out of room.

The WD Smartware will not delete a file from your backup, even if you delete the file from the computer. The software will keep the data.