Directory linking

[Fiel]

What if I want to use directory linking as a method of backup?

Say I have my favorite pictures on my C drive. I want to link my favorite pictures onto my D drive so there are two copies of the same file. The functionality that I want is that if either copy should be destroyed, the other copy will still exist. I'm not looking to do RAID because I only want this to apply to one directory. As an added feature, I'd also like to be able to determine which files in the primary directory are linked and which ones are not. Some I'd like to make sure are saved, and others I really don't care about. To sum it up, I want a one-way hard link.

Hard and symbolic links don't do what I'm looking for. Can anyone help me find how to do what I'm looking for?

FOO ------> [DATA]
              ^
              |
              |
              |
BAR --> [COPY OF DATA]

If FOO changes, BAR should change too. 
But if BAR changes, FOO should not change.

EDIT: Found what I was looking for --> SyncToy

[rassilon]

AFAIK, you're looking for RAID1. I'm not an expert, but links don't work like that. Soft links are one file with appearances elsewhere, and if an appearance gets deleted the original remains; hard links are one file with simultaneous presence elsewhere, and if any of them gets deleted, they all go.

I'd be interested to know if you find a solution that doesn't involve additional software (such as robocopy, in the Windows world).