Looking for a way to install and run OS X on an external hard drive? This can be useful for a couple of different reasons. Firstly, it allows you to run another copy of OS X without needing any additional Mac computer.
Also, since you can run a full copy of OS X on the external drive, it can be used for troubleshooting purposes on other Macs or it can be as a kind of virtual OS X. I’ve already 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.
In this article, I’ll walk you through the requirements and steps to install OS X onto an external hard drive.
Mar 18, 2020 Connect your external drive into the appropriate port on your Mac. Turn on your Mac. Hold down the Option key as soon as you hear the startup chime. Select the external drive with the clone backup on it from the list of systems to start up your computer.
The first thing you’re going to need to do is format the external hard drive properly. 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.
Under External in the left hand menu, click on your external hard drive and then click on the Erase button. Make sure you backup any data before you erase the drive. When you click Erase, a dialog will pop up where you can configure some options.
Give your drive a name, choose OS X Extended (Journaled) for Format and GUID Partition Map for Scheme. It should only take a minute or two for the drive to be erased and reformatted. Now your drive is ready for OS X.
There are two ways you can install OS X on to your external hard disk: by reinstalling OS X from the OS X Utilities repair screen or by downloading OS X from the App Store and running the installer. I’ll show you both methods in case one isn’t working for you.
The easiest way is to download OS X from the App Store. Once you open the App Store, you’ll see a link on the right for the latest version of OS X (El Capitan as of this writing).
Go ahead and click the Download button to start downloading the installer. Note that if you already have that version of OS X installed, you’ll see a popup message appear asking if you still want to continue or not. Just click Continue.
Once it has been downloaded, just double-click the installer, which will be located in the Applications folder.
Keep clicking past the license agreement, etc., until you get to the screen that asks you which disk to install OS X on. By default, it is set to MacBook.
Click on the Show All Disks button and you’ll see an icon for the different disks and partitions on the Mac. I named my external hard drive OS X and that shows up in the middle.
You can also tell it’s an external hard disk because it uses the icon with the orange hard drive. 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.
At the end of this article, I’ll show you how to boot up to the external hard drive, so skip down if you ended up using the App Store method. Note that by default, the Mac will start booting up directly to the external hard drive until you change it.
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.
Using this method, you’ll have to login using your Apple ID and password so that the entire OS X installer can be downloaded off of Apple’s servers. Whichever method you choose, it will take anywhere from 15 to 30+ minutes to install OS X onto your external hard drive.
While OS X is installing, your computer will restart a couple of times. Note that when it finally boots into OS X, that is the version running off 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 do that, you should see at least four icons. In my case, I have five because I have Windows installed using Boot Camp. Anyway, 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.
Use the arrow keys to select which drive to boot from and then simply 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!
It is vitally important that you back up your Mac. Whether you do so locally using Time Machine, sending it to a cloud service, or installing a duplicate creation program (or all three). There is nothing more important than backing up your computer in case an unfortunate event happens so you don't lose your precious data.
One of the easiest methods is locally, using Time Machine. Another is by backing up your data via a cloud-based service, like Backblaze or CrashPlan. Here, we're going to explain how to clone your Mac using a program like SuperDuper! or Carbon Copy Cloner.
Local backups through Time Machine, cloud-based backups, and clones all serve a great purpose to keep your data safe in case of an unfortunate even that renders your Mac useless (even temporarily). The thing that makes cloning different is that you can create a bootable copy of your entire hard drive, which means you can access everything on one Mac through another simply by exporting it to an external drive, connecting the drive to the other Mac, and then selecting it from the Startup menu.
Clones are great to have around if, for example, you have to take your Mac in for repairs, but still need to continue working while it's out. You can use the cloned copy while it's in the shop.
Most cloning programs have additional features that include the ability to make regularly scheduled backups. This is ideal since, if something happens to your computer, you aren't necessarily going to want to restore from a year-old backup. I highly recommend investing in these additional features if they are offered with the cloning program you are using (for example, SuperDuper! is free to clone, but costs a licensing fee of $28 for scheduling, smart updates, sandboxes, and scripting).
Before you get started, make sure you have an external hard drive with enough storage to fit everything on your Mac. The smartest solution is to use a portable hard drive.
You'll also need to download and install your cloning program. I'm using SuperDuper! from Shirt Pocket for this process. Most cloning programs operate pretty much the same. They will always have a detailed how-to guide to walk you through the steps.
You'll need to start with a clean external hard drive in order to make a bootable drive for your cloned backup.
Double-click on Disk Utility to open it.
Source: iMore
Click the Erase tab at the top of the window.
Source: iMore
Close the Disk Utility window.
Source: iMore
Your hard drive is now formatted for cloning your Mac.
After you've downloaded and installed your cloning program, you'll need to open it to get started. I'm using SuperDuper! to make a clone for this guide, so I'll reference it here.
Note: You'll need your administrator password in order to make a clone of your Mac.
Select the external hard drive from the drop-down menu next to 'to.'
Source: iMore
Click Copy Now to begin the process.
Source: iMore
Click OK when the process is complete.
Source: iMore
Most cloning programs will operate the same, general way. If you don't understand the process for the program you have chosen, refer to the user guide.
If there is any reason you end up needing to restore your Mac from a backup, you can use a clone to do so.
Once the backup has finished restoring, restart your computer.
If you want to work on your backup on another computer while it's in the shop, you can boot it up from the startup menu.
Important: You'll need to partition your hard drive in order to boot your clone as a separate startup disk. Be sure to do that before following the steps below.
Now, you can use the clone to restore files to your partitioned drive.
Do you have any questions about how to clone your Mac so you can use it as a backup? Put them in the comments and I'll help you out.
Updated March 2020: Updated for MacBook Air.
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