MacOS – OS X: Set up one folder as “extension” of another, symlink-style

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I have two folders on two different Volumes:

  • /Volumes/SSD/my-important-folder
  • /Volumes/HDD/my-extension-of-important-folder

In the second folder I put large files and folders so they do not take up all the space on the SSD. In order to have everything in one place I create symlinks from the first to the second folder, like so:

/Volumes/SSD/my-important-folder/big-file is a symlink to /Volumes/HDD/my-extension-of-important-folder/big-file

This is useful because big files get stored on the HDD yet they are available as if they were stored on the SSD. But this has the disadvantage that I have to create a symlink for every file oder folder that I add to the folder on HDD.

It would be really useful if I could say to the OS: if I call a file that is not in /Volumes/SSD/my-important-folder, please look it up in /Volumes/HDD/my-extension-of-important-folder.

The folder on the HDD would then be a real extension of the folder on the SSD.

Can this be done? I am running OS X 10.9.1

Best Answer

As far as I know, you can't do that directly but I'm not sure I understand why you'd want to?

Why not just symlink the entire folder and never worry about it going forward?

If it's important to you that it's only large files that are moved to the HDD, you could create a Folder Action in Automator and run a bash script that checked file size and based on that moved and created the symlink automatically (I'm assuming you've got some tech skill since you know what symlink even is :) With that said, I'd be happy to post more detailed instructions if need be).

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