OS X on an external drive can be used as a virtual OS X that can be used for troubleshooting purposes on other Macs or it can be used as a kind of backup or virtual OS X. I’ve written about how you can install OS X in VMware Fusion, but that takes up space on your Mac. Using an external drive, you can save space on your Mac, though it might be a bit slower if you are using USB 2.0.

Requirements: -An external hard drive with at least 2TB storage capacity -OS X Yosemite 10.12.6 or later -A USB drive with at least 8GB storage capacity -An Apple ID or a similar account to access the computer Steps:

  1. Connect your external hard drive to your computer.
  2. Open Finder and click on the Go button in the top left corner of the screen.
  3. Type “diskutil list” and hit return to see the list of devices connected to your computer.
  4. In this example, I’m using an external hard drive with 2TB storage capacity, so I’ll type “diskutil list -2t” into the Finder and hit return to see that it has been added as a device in the list.
  5. If you want to add more devices, just type them in after the “diskutil list” command and hit return to continue listing devices.
  6. Now open Terminal and type “sudo diskutil addvol -size 2t /dev/sda1” (without quotes) and hit return to continue adding devices one by one until you’ve added all of your desired ones (in this example, I’ve added two drives).
  7. Finally, type “sudo diskutil removevol -size 2t /dev/sda1” (without quotes) to remove all of your desired drives from your computer’s storage space (in this example, I’ve removed two drives).

Format External Hard Disk

Next, you’re going to need to format the external hard drive. The file format has to be Mac OS X Journaled and you have to use the GUID partition map. To do this, open Disk Utility and connect the drive to your Mac.

If you want to erase your external hard drive, first make sure you have a backup of your data. Then, in the Erase dialog, be sure to configure some options to ensure your data is erased completely.

The drive you just reformatted is called “OS X Extended (Journaled)”. The drive’s GUID Partition Map is called “Scheme”.

Install OS X

reinstall OS X from the OS X Utilities repair screen: To reinstall OS X from the Utilities repair screen, open the Utilities menu and select “Repair Disk.” In the “Repair Disk” window, click on the “Install OS X” button. After installation is complete, you will be able to access your computer from the Utilities menu. download OS X from the App Store and run the installer: To download OS X from the App Store and run the installer, open Safari and type “OS X Installer.” After installation is complete, you will be able to access your computer from Safari.

If you’re looking for the latest version of OS X, you can find it on the App Store.

If you’re not already using OS X, you’ll need to install it first. Then, follow the prompts to start the installer. If you already have OS X installed, you’ll see a popup message asking if you still want to continue or not. Just click Continue.

To install the app, just double-click the installer file that was downloaded. The installer will be located in the Applications folder. ..

If you’re using an Apple computer, you can install OS X on the following disk:

  1. The MacBook hard drive.
  2. A removable drive (like a DVD or USB drive).
  3. A digital media player like an Xbox 360 or PlayStation 4.

The external hard drive that I named OS X is in the middle of the Mac’s disks and partitions.

You can tell that the external hard drive is an OS X external hard drive by the orange hard drive icon. Click Continue and then follow the instructions to complete the installation. Note that your computer may restart during the install and you don’t have to do anything. OS X will automatically continue installing onto the external hard drive rather than booting up to your internal version of OS X.

If you’re using the Mac to access your external hard drive, you can boot up to it by following these steps:

  1. Open the System Preferences panel and select the Hard Drive tab.
  2. In the Hard Drive section, select the external hard drive you want to use as your primary hard drive. If you’re using a different external hard drive for different purposes, select that instead.
  3. Click on the Change button and then enter a new name for your external hard drive in the Name field. The default name is “Macintosh HD”.
  4. Click on OK to save your changes and close System Preferences.

The second method to install OS X is to restart the Mac and press and hold the COMMAND + R keys. This will load up OS X Recovery.

The OS X Utilities screen will appear and here you want to click on Reinstall OS X. Again, you’ll go through some basic screens, but when you get to the hard disk screen, click on Show All Disks again.

To install OS X Yosemite on an external hard drive, you will need to login with your Apple ID and password. The installation process can take anywhere from 15 to 30 minutes, depending on your computer’s hardware. ..

OS X will restart a few times during installation. Once it’s finished, the OS X you’re using is the one on your external drive. To switch back and forth between the internal and external drive, you have to restart your computer and hold down the OPTION key. ..

When you use Boot Camp to install Windows, you should see at least four icons. The grey MacBook and Recovery 10.11.2 icons are for my internal OS X and the orange OS X and Recovery 10.11.3 are for the version installed on my external drive.

To boot your Mac from a USB drive, first make sure that the drive is formatted to Mac OS Extended (Journaled) format. Next, use the arrow keys to select which drive you want to boot from and then press Enter. If you have a newer Mac and a USB drive that supports USB 3.0, everything should run fairly fast. Overall, it’s a fairly straight-forward process and took me less than an hour to get everything working. If you have any questions, feel free to comment. Enjoy! ..