Backing up an external portable HDD efficiently

I have an external USB HDD all data to be used on multiple PCs. These data backs up for security reason. Now I do it manually, the other usb disk, in a way which is quite useful, but quite inefficient and laborious.
Mainly because data size of about 400GB. These are photos, xls files, documents, drawings. Simply files that I am continuously working on them.
I tried more online or other backup solutions, not suit me. After some time they wasn't updated and controllable as multiple versions of the same file.
It can be done differently? Is there any sw which when run can compare two different usb hdds on the base of existing database and update the second hdd by the first one?
This means only the changed files updated by more recent data (differential or incremental backup).
Parameters: no resident program, ease of use. What is your experience of this kind?
thanks for the tip
Peter

 

There may be free software that can do what you want though I've never found it so I use WinRAR. It meets all of your needs but irritatingly does not have a built in scheduler. That can be worked around using Task Scheduler though. Sync software meets some of your requirements but not multiple versions.

 

you might want to look at http://www.cobiansoft.com/cobianbackup.htm have used this and it is really good for full and incrementals.
and / or
Foldermatch from SaltyBrine. I use folder match to sync files, you can select to over write the old file very easily. Free trial but worth the $$$.

There is a free file sync on sourceforge.net you might try for free.

Also this one popped up - I have not tried it yet Create Synchronicity