Use an external SSD as your startup disk with your iMac or Mac mini
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 a startup disk can give your Mac additional performance for system responsiveness, apps, startup, and more.
Compatible Mac models
Using an external SSD as a startup disk is supported by most Intel-based Mac models that include an Apple hard disk or Fusion Drive, USB 3 or Thunderbolt 3 ports, and are running the latest compatible version of macOS. Learn how to update the software on your Mac.
These Mac models are compatible with using an external SSD.
iMac
- iMac (Retina 5K, 27-inch, 2019)
- iMac (Retina 4K, 21.5-inch, 2019)
- iMac (Retina 5K, 27-inch, 2017)
- iMac (Retina 4K, 21.5-inch, 2017)
- iMac (21.5-inch, 2017)
- iMac (Retina 5K, 27-inch, Late 2015)
- iMac (Retina 4K, 21.5-inch, Late 2015)
- iMac (21.5-inch, Late 2015)
- iMac (21.5-inch, Mid 2014)
- iMac (27-inch, Late 2013)
- iMac (21.5-inch, Late 2013)
- iMac (27-inch, Late 2012)
- iMac (21.5-inch, Late 2012)
Mac mini
- Mac mini (Late 2014)
- Mac mini (Late 2012)
Supported external SSD products
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. To check how much storage you're using:
- macOS Ventura and later: Go to System Settings > General > Storage
- macOS Monterey and earlier: Go to the Apple menu > About This Mac > Storage
Recommended external SSDs, along with any required accessories, are listed below.
iMac models introduced in 2017 and 2019
For iMac models introduced in 2017 and 2019, these computers have Thunderbolt 3 (USB-C) ports and USB-A ports. Recommended external SSDs for these models:
*The OWC Envoy Pro FX is a Thunderbolt SSD. Thunderbolt SSD models have higher data transfer rates than USB-C 3.2 SSDs, which could be useful if you often work with professional software or large libraries.
iMac models introduced in 2012 through 2015 and Mac mini models introduced in 2012 and 2014
For iMac models introduced in 2012 through 2015, and Mac mini models introduced in 2012 and 2014, these computers have USB-A ports that supports USB 3. Recommended external USB 3 SSD configuration for these models:
For the best performance and reliability, it's recommended to use the external power adapter. It ensures the SSD receives reliable power while it's used as your startup disk.
Note: While many external SSDs may work as a startup disk for Mac, some models don’t include the correct chipset, connection type, or macOS startup disk functionality. If you're considering a different product, check with the manufacturer to confirm support for Mac startup disk use and that a compatible cable is included.
Connect and erase the external SSD
Connect the external SSD to your Mac using the cable that came with it to a compatible port on your Mac.
In Disk Utility on Mac, you can erase and reformat the external SSD to use with your Mac. Erasing a storage device deletes everything on it.
- In the Finder, choose Go > Utilities, then double-click the Disk Utility icon. (Disk Utility is located in the /Applications/Utilities folder.) Alternatively, click Launchpad in the Dock, type Disk Utility in the search field, then click the Disk Utility icon.
- Choose View > Show All Devices.
- In the sidebar, select the external SSD device you want to erase, then click the Erase button.
- Click the Scheme pop-up menu, then choose GUID Partition Map. (If the Scheme pop-up menu isn’t available, make sure you selected the storage device you want to erase—it’s at the top of the hierarchy.)
- Click the Format pop-up menu, then choose APFS. (If APFS is not shown, choose GUID Partition Map first, then change the format to APFS.)
- Enter Macintosh HD as the name.
- Click Erase, then click Done.
Install macOS to the external SSD
Apple recommends using the latest (newest) macOS that is compatible with your Mac. macOS updates and upgrades help to maintain your computer's security, stability, and compatibility, and they include the latest features and built-in apps.
Before installing, it’s a good idea to back up your Mac.
To download macOS, see the Apple Support article How to download and install macOS - Apple Support, and look under the "Use the App Store" section to find the version of macOS compatible with your Mac:
macOS Sequoia 15 is compatible with these computers
- iMac (Retina 5K, 27-inch, 2019)
- iMac (Retina 4K, 21.5-inch, 2019)
macOS Ventura 13 is compatible with these computers
- iMac (Retina 5K, 27-inch, 2017)
- iMac (Retina 4K, 21.5-inch, 2017)
- iMac (21.5-inch, 2017)
macOS Monterey 12 is compatible with these computers
- iMac (Retina 5K, 27-inch, Late 2015)
- iMac (Retina 4K, 21.5-inch, Late 2015)
- iMac (21.5-inch, Late 2015)
- Mac mini (Late 2014)
macOS Big Sur 11 is compatible with these computers
- iMac (21.5-inch, Mid 2014)
macOS Catalina 10.15 is compatible with these computers
- iMac (27-inch, Late 2013)
- iMac (21.5-inch, Late 2013)
- iMac (27-inch, Late 2012)
- iMac (21.5-inch, Late 2012)
- Mac mini (Late 2012)
When the macOS installer opens and you're asked to choose where to install, click Show All Disks, then select the new external SSD before continuing.
Move your content to the external SSD
You can use Migration Assistant to copy all of your documents, apps, user accounts, and settings to the external SSD from the internal disk or your Time Machine backup.
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.
Finish up
After Migration, change your startup disk to set the external SSD as the default startup disk.
- In macOS Ventura or later: Choose Apple menu > System Settings, click General in the sidebar, then click Startup disk on the right. Click the icon of the disk you want to use, then click Restart.
- In macOS Monterey or earlier: Choose Apple menu > System Preferences, then click Startup disk. Click the icon of the disk you want to use, then click Restart.
Next, rename your internal disk to a name other than Macintosh HD.
Note: You may need to configure certain settings again, such as Time Machine.
About the internal disk
After setting the external SSD as the startup disk and migrating your data, you can erase the internal disk.
- In the Finder, choose Go > Utilities, then double-click the Disk Utility icon. (Disk Utility is located in the /Applications/Utilities folder.) Alternatively, click Launchpad in the Dock, type Disk Utility in the search field, then click the Disk Utility icon.
- Choose View > Show All Devices.
- In the sidebar, select the internal disk device you want to erase, then click the Erase button.
- Click the Format pop-up menu, then choose APFS.
- Enter a name.
- Click Erase, then click Done.
If you plan to leave the internal disk as-is with macOS on it, exclude the internal disk from Spotlight indexing. Learn how to on macOS Ventura 13 and later or macOS Monterey 12 and earlier.