Running apps from an external drive: what works, what breaks, and what to move instead
Many Mac apps run fine from an external SSD, but App Store apps and anything with a helper may not. What to move, what to leave, and where the real space is.
Your Mac is full, and the Applications folder has a 12 GB game and a 4 GB video editor. Moving them to an external SSD seems obvious. Sometimes it works perfectly, and sometimes the app stops updating or will not launch. Knowing which is which saves an afternoon.
What usually works
- Apps you downloaded from a website and installed by dragging to Applications. Most are self-contained and run from anywhere.
- Games from launchers that let you choose a library folder, such as Steam. Set the library on the external drive from inside the launcher. See Steam games taking up space.
What usually does not
- App Store apps. They update themselves only in Applications. Moved elsewhere, they stop updating, and some refuse to open.
- Apps with installers, such as Microsoft Office and Adobe apps. They put helpers and background services in system folders that point to the original location.
- Apps you open at login or that sync, like Dropbox. When the drive is unplugged, they fail.
The better win: move the data, not the app
The app itself is rarely the big part. What grows is its data: game saves and downloads, a Photos library, a video project, a music sample library. Those usually have a setting to change their location, and moving them is supported.
| App type | Move this instead | Where to change it |
|---|---|---|
| Photos | The library | Hold Option when opening Photos |
| Music creation | Sound library | Inside the app's sound library settings |
| Video editors | Projects and caches | Project or library settings |
| Games | The game library | The launcher's storage settings |
Check what an app really takes
# App bundle size
du -sh /Applications/SomeApp.app
# Its support files, usually larger
du -sh ~/Library/Application\ Support/SomeApp ~/Library/Containers/*SomeApp* 2>/dev/nullApplication Support is where most of it lives. To find apps you never open at all, see finding unused apps.
Related: X-Plane taking up space on Mac.
Common questions
Can I install Mac apps on an external drive?
Many downloaded apps run fine from an external SSD. App Store apps and apps with installers often do not, and may stop updating.
Why won't my app open after moving it to an external drive?
It probably relies on helpers or updates that expect it in Applications. Move it back, and move its data to the external drive instead.
What should I move to an external drive instead of apps?
App data: photo libraries, video projects, game libraries and sound libraries. They are usually bigger, and most apps let you change where they live.