I'm a little bit confused, what's the best way to back up files, is it  fff or 3fr; fff files sizes are twice the size, so would assume more date is stored. I know the flexcolour software saves the 3fa as compressed raw files, just got me thinking that’s all? 
 
I'm starting a big personal project, were I'm converting all images to  dng, but want to keep all originals as well. First lot of the project I saved  as 3fa (downloaded from card), second lot are now fff as I downloaded them  from back as I lost card reader, (both were shot on CF card)?  
 
When I first started shooting digital (a while back now), I didn't  bother saving my raw files, just converted to tiffs, big mistake, which is  making me think I should keep fff or 3fa files as well as dng files. That’s  my thinking anyway, I'm sure some people will think other wise.  
 
Any advice/comments would be appreciated. Thanks