Boot Mac Mini from external drive

Use an external SSD as your startup disk with your iMac or Mac mini

Last modified: Jan 2, 2023 7:36 PM

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Your USB 3-equipped Mac with a hard disk or Fusion Drive can have improved system performance by connecting to an external solid-state drive (also known as an SSD).

An external SSD as your startup disk can give your Mac additional performance for system responsiveness, apps, startup, and more. An SSD will make your Mac 10 to 40 times faster for storage, and in turn, make your entire Mac faster and more capable.

These Mac models are compatible with an external SSD startup disk:

• iMac (21.5-inch, Late 2012)
• iMac (27-inch, Late 2012)
• iMac (21.5-inch, Late 2013)
• iMac (27-inch, Late 2013)
• iMac (21.5-inch, Mid 2014)
• iMac (Retina 5K, 27-inch, Late 2014)
• iMac (Retina 5K, 27-inch, Mid 2015)
• iMac (21.5-inch, Late 2015)
• iMac (Retina 4K, 21.5-inch, Late 2015)
• iMac (Retina 5K, 27-inch, Late 2015)
• iMac (21.5-inch, 2017)
• iMac (Retina 4K, 21.5-inch, 2017)
• iMac (Retina 5K, 27-inch, 2017)
• iMac (Retina 4K, 21.5-inch, 2019)
• iMac (Retina 5K, 27-inch, 2019)
• Mac mini (Late 2012)
• Mac mini (Late 2014)

The Mac models above must be equipped with an Apple hard disk or Fusion Drive for an external SSD to provide additional performance.

To check, open Disk Utility (located in Applications > Utilities), and within Disk Utility, select View > Show All Devices, and look for an entry titled “APPLE HDD” or "Fusion Drive".

It's important to use an external SSD with enough storage for your documents, photos, music, and apps, as well as extensive video libraries and large data files. Additionally, an external SSD should utilize USB 3.2 technology and have the functionality of being used as a startup disk for Mac.

A recommended external SSD is the Crucial X8 Portable SSD - Crucial.

The Crucial X8 SSD listed above has capacities from 1 TB - 4 TB, along with fast speeds and reliable endurance.

Although many external SSDs may work as an external SSD startup disk for Mac, some may not have the correct connection or startup disk functionality.

If you purchase an external SSD other than what is recommended above, check with the manufacturer to find out if it uses USB 3.2 technology and can be used as a startup disk for a Mac computer.

Before starting, it is recommended to use Time Machine, the built-in backup feature of your Mac, to automatically back up your personal data, including apps, music, photos, email, and documents. Having a backup allows you to recover files that you later delete or can't access.

To start your first Time Machine backup, connect an external storage device. If you need one, you can use another Crucial X8 Portable SSD - Crucial.

To learn more on using Time Machine, see Back up your Mac with Time Machine - Apple Support.

Additionally, you can use iCloud, which can automatically store your photos, calendars, contacts, notes, passwords, and more. And it includes iCloud Drive, which can store documents, desktop files, and other files of your choosing. To access those files, you just need to be signed in to iCloud. 

To learn more on using iCloud, see:

• Upgrade to iCloud+ - Apple Support
• Set up iCloud Drive - Apple Support
• Add your Desktop and Documents files to iCloud Drive - Apple Support
• Set up and use iCloud Photos - Apple Support

To start, connect your external SSD to your Mac.

If you have an iMac (2012-2015), or a Mac mini (2012-2014), connect the external SSD using a USB Type-A port. If you have an iMac (2017-2019), connect the external SSD using a USB Type-C port.

To learn more, see Identify the ports on your Mac - Apple Support.

If after you connect the external SSD you plan to use as your startup disk you receive a message asking if you would like to use the external SSD as a Time Machine backup drive, click Don't Use.

Additionally, don’t install any software from the external SSD manufacturer. 

Next, you need to erase and reformat your external SSD. Open Disk Utility (located in Applications > Utilities), and within Disk Utility, select View > Show All Devices. Select the external SSD entry at the top of the list (its name will also end in "Media").

Click Erase, and make sure the name, format, and scheme are as follows:

• Name: Macintosh HD
• Format: APFS* (If APFS is not shown, choose GUID Partition Map first, then change the format to APFS)
• Scheme: GUID Partition Map

Click erase. After a few moments, you should see a new Macintosh HD volume on your external SSD.

*-If you are using macOS Sierra or earlier, choose Mac OS Extended (Journaled) instead.  

After erasing, you can install macOS on your external SSD. Make sure to download the latest compatible version of macOS for your Mac.

These iMac and Mac mini models are compatible with macOS Catalina: 

• iMac (21.5-inch, Late 2012)
• iMac (27-inch, Late 2012)
• iMac (21.5-inch, Late 2013)
• iMac (27-inch, Late 2013)
• Mac mini (Late 2012)

Get macOS Catalina here: How to download macOS - Apple Support.

These iMac models are compatible with macOS Big Sur:

• iMac (21.5-inch, Mid 2014)
• iMac (Retina 5K, 27-inch, Late 2014)
• iMac (Retina 5K, 27-inch, Mid 2015)

Get macOS Big Sur here: How to download macOS - Apple Support.

These iMac and Mac mini models are compatible with macOS Monterey:

• iMac (21.5-inch, Late 2015)
• iMac (Retina 4K, 21.5-inch, Late 2015)
• iMac (Retina 5K, 27-inch, Late 2015)
• Mac mini (Late 2014)

Get macOS Monterey here: How to download macOS - Apple Support.

These iMac models are compatible with macOS Ventura:

• iMac (21.5-inch, 2017)
• iMac (Retina 4K, 21.5-inch, 2017)
• iMac (Retina 4K, 21.5-inch, 2019)

Get macOS Ventura here: How to download macOS - Apple Support.

When the installer opens and you're asked to choose where to install, click Show All Disks, then select the new external SSD before continuing the install.

When your Mac restarts to the external SSD, follow the prompts in Setup Assistant. When asked how you want to transfer your information, select the option to transfer from a Mac, Time Machine backup, or startup disk. Then click Continue. Select your Time Machine backup or internal hard disk, then click Continue. Continue to follow the steps to restore. Large transfers might need several hours to complete.  

After Migration, change your startup disk to set the external SSD as the default startup disk and rename the internal disk to a name other than Macintosh HD.

macOS Ventura

On your Mac, choose Apple menu > System Settings, click General in the sidebar, then click Startup Disk on the right. (You may need to scroll down.)

Click the icon of the disk you want to use, then click Restart.

macOS Monterey and earlier

1. On your Mac, choose Apple menu > System Preferences, then click Startup Disk.
2. If the lock at the bottom left is locked, click it to unlock the preference pane.
3. Click the icon of the disk you want to use, then click Restart.

Next, you need to rename your internal disk to a name other than the name you're using for your external SSD, which should be Macintosh HD.

Additionally, after Migration, you may need to configure certain settings again, such as Time Machine.

After a successful setup and Migration to the external SSD, you can erase* the internal disk. Open Disk Utility (located in Applications > Utilities), and within Disk Utility, select View > Show All Devices. Select the entry titled “APPLE HDD”. Click Erase, and make sure the format and scheme are as follows:

• Format: APFS
• Scheme: GUID Partition Map

Click Erase. After a few moments, you should see a new, empty volume on your internal disk. 

*- If you plan to leave the internal disk as-is with macOS on it, exclude the internal disk from Spotlight indexing: Change Spotlight preferences on Mac - Apple Support. Additionally, rename the internal disk to a name other than Macintosh HD.

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