Alias, copy, duplicate or symlink: which ones actually use more space on a Mac
An alias is tiny, a copy on the same disk may be free, and a copy to another drive is full size. What each one costs and how to check which you have.
You want a file to appear in two places. Depending on how you do it, the second one costs nothing, a few KB, or its full size. It helps to know which.
| Method | How | Space used |
|---|---|---|
| Alias | Control-click, Make Alias | A few KB |
| Symbolic link | ln -s in Terminal | Almost nothing |
| Duplicate on the same disk | Command D in Finder | Nothing at first, until you edit one |
| Copy to another disk | Drag to a different drive | Full size |
| Download or export again | Save a new file | Full size |
Aliases and symbolic links
Both point at the original. An alias follows the file if you move it; a symbolic link does not. Delete the original and both stop working. They are the right tool for having one folder show up in several places.
ln -s ~/Documents/Taxes ~/Desktop/TaxesDuplicates on the same disk are clones
On a modern Mac, Finder's Duplicate makes an APFS clone: the copy shares the original's bytes until one of them changes. So duplicating a 10 GB video is instant and free. The catch is that Finder shows both at full size, and deleting one frees nothing. APFS clones and copies goes further.
Copies elsewhere are real copies
Copying to another drive, downloading the same file twice, or saving an export makes independent files. Those are the duplicates that cost space. Finding duplicate files finds them.
# Is this an alias or a link? A link shows an arrow in ls
ls -l ~/Desktop/TaxesCommon questions
Do aliases take up space on a Mac?
Only a few KB. An alias is a small pointer to the original file, not a copy.
Does duplicating a file on a Mac double the space used?
Not at first. On APFS, a duplicate on the same disk shares the original's data until one of them is changed.
What is the difference between an alias and a symbolic link?
An alias follows the original if it moves. A symbolic link points at a path and breaks if the original is moved or renamed.