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.
Format External Hard Disk
Mac Disk Utility is a powerful built-in application in Mac OS that has undergone a series of changes with every major OS update. Many Mac users have complained that using Mac Disk Utility to resize a Mac Volume is no longer easy. However, being an experienced Mac expert, we feel its interface is user-friendly and easy to use. Apple has come up.
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.
Install 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.
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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!
If you've always wanted to partition your Mac's hard drive so you can run a separate operating system — including the launch of macOS Big Sur — in tandem with your current one, it's surprisingly easy to do so thanks to Apple's built-in disk utility program. Here's how to partition your Mac.
What is a disk partition?
Partitioning your Mac is basically splitting your hard drive into separate, usable systems. It makes it possible to run two separate operating systems on one device, like Windows and macOS, or two versions of macOS (like Catalina and Big Sur).
Note: If you want to run Windows on your Mac, Apple's Boot Camp assistant will automatically make a partition for you. Here's how to install Windows.
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It is important to note that partitioning your hard drive also splits up your available hard drive space. Each partition will take up a portion of your usable storage. So, if you are running low on storage capacity on your hard drive, we don't recommend partitioning.
Before you start
The most important thing to do before making any changes to your hard drive is to back it up. Seriously. Back it up. Please. Time Machine is the easiest way to back up your data if you don't already have another system in place.
Second, make sure you have enough free disk space to properly run a secondary operating system. Shoot for at least 30GB free, though I recommend closer to 50GB if you have it available.
How to create a partition on your Mac
Disk Utility will check the disk and make changes. This will take several minutes.
How to switch partitions
You can switch to the new partition, install the current macOS, and then download and install macOS Catalina from there.
You can also restart your Mac and press the Option Key when you hear the startup chime. This will take you to the Startup Manager and you can select your drive from there.
You will then be asked to install macOS. This will install the latest available macOS onto the partitioned hard drive. You may have to install an older version of macOS before updating it to the more recent version you want to run.
If you are testing a beta version of macOS, you'll first install whatever the current version is. Then, you can then install the macOS beta.
How to download the developer beta of macOS Big Sur
Once you've updated your partitioned Mac with macOS Catalina, you can download and install the developer beta of macOS Big Sur. You need a developer account and probably some patience. Developer betas are often a bit complicated to install. We've got a guide to help you out.
Mac Os X Filevault Just For A Removable Disk DriveAny questions?
Do you have any questions about installing a partition or downloading a new operating system onto a partitioned drive? Let us know in the comments. If you're having trouble partitioning your hard drive, be sure to check out our forums for help!
Updated June 2020: Updated for the developer beta of macOS Big Sur.
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