Redirect Document files to external drive

You can create a hard link to the external drive, but that is not recommended in case the drive fails or is otherwise not available. My recommendation here would be to create an alias in your documents folder to the external drive, which you can then easily access. To do this select the external drive on your desktop and press Command-L, and then drag the resulting alias to your Documents folder.

Not a hardlink, but rather a symbolic link. Hardlinks can only point to things in the same physical file system.

As Topher Kessler says, you could just create an Alias. Copy your entire Documents folder to the external disk (you are going to be backup of that external disk, RIGHT? Once your are satisified that all your Document files are really on the external disk, you can rename the original Documents folder to something else, then holding Command-Option, drag the external disk Document back to your home folder. This should create an alias and should be extremely fast. If it starts copying the data back, then something went wrong.

If you are happy that new files get created on the external disk, you can now delete the renamed Documents folder to get back your space.

Creating a symbolic link would be either down from the Terminal app using Unix commands, or via a 3rd party app that offers that support (MacUpdate.com)

Sorry...you're correct I meant a symbolic link.