Macos – Using an external drive for application storage in Mac OS X 10.10

external hard drivemacososx-yosemitessd

I have just upgraded my Mac Mini (Mac Mini 2.6Ghz i7 16Gb RAM) to use a 256GB SSD for the boot drive. I have successfully installed Mac OS X 10.10 Yosemite as my OS, with a clean installation.

I intend to use this for music production. This is my first Mac for the purpose. I don’t want to clog up the SSD with other stuff, so would like programs such as iPhoto to use my external USB3 hard drive. Is there a way to make all programs use the external drive as their default storage location?

I don’t want it to start auto-importing the photos from my iPhone to the SSD when I connect it for example. My external drive has 2TB of storage space which I’d rather use. I would also like my audio programs to record the audio to the external drive, keeping the main program on the SSD. I intend to use Ableton Live Suite 9.

Best Answer

When I’ve done this sort of setup in the past, I’ve generally located my user’s home directory on non-SSD storage. This is a bad idea in your case since that could more or less cripple your user account when you login and your SSD is missing.

I suggest you first make yourself an admin account called “backup” or something, in case you seriously screw up your main account - and from which you can tweak the main account.

Then I’d login as the backup user and move your ~/Desktop, ~/Downloads, ~/Photos, ~/Music, etc directories on to your preferred storage. Finally, symlink the new locations to your home directory..

For example:

  1. mkdir -p /Volumes/USB-Drive/Users/doc/
  2. mv /Users/doc/Desktop /Volumes/USB-Drive/Users/doc/Desktop
  3. mv ....
  4. ln -s /Volumes/USB-Drive/Users/doc/Desktop /Users/doc/Desktop
  5. ln -s ....

Similarly, you could do the same for your /Applications directory, though that’s dangerous because some applications your System Preferences, Terminal, etc could be missing when you break your USB drive. Thus, I recommend you leave /Applications on the SSD and create an Applications dir on the USB drive, then move in apps on an individual basis after install and either just leave them there entirely or additionally sym link them in to /Applications as well.

I highly recommend you keep time machine backups of your entire setup somewhere safe. Storing your user data on an external drive is kind of a sketchy proposition, unless you're quite careful. If your machine has an optical drive, you should consider getting a kit to replace it with an adapter that lets you install a secondary hard drive, then you could use that for your user data.

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