How to Use an External Hard Drive as the Main Drive on a Mac

Using an external hard drive as the main drive on a Mac involves a few steps including formatting the drive, transferring the operating system, and configuring your Mac to boot from it. This guide will walk you through the process step-by-step.

Introduction

Mac users often seek ways to increase storage, gain flexibility, or extend their data safety by using external drives. An external hard drive can serve as a primary drive if configured correctly. This article covers how to make an external hard drive bootable as the main drive on a Mac.

Step 1: Format the External Hard Drive

Connect the Drive

First, you need to connect your external hard drive to your Mac:

Plug your external hard drive into your Mac using the appropriate USB cable.

Open Disk Utility

Open the Applications folder. Navigate to Utilities and open Disk Utility.

Select the Drive

In Disk Utility, select your external hard drive from the list on the left panel.

Erase the Drive

Click on the Erase button. Choose a format. For solid-state drives (SSDs), select APFS. For hard disk drives (HDDs), choose Mac OS Extended (Journaled). Name the drive and click Erase. This will delete all data on the drive, so make sure to back up any important files first.

Step 2: Install macOS on the External Drive

Download macOS

Open the App Store and download the latest version of macOS or your desired version.

Create a Bootable Installer (Optional)

If you prefer to use a USB drive to install macOS, create a bootable installer using a USB drive. Follow Apple's instructions for creating a bootable installer.

Install macOS

Open the downloaded macOS installer. When prompted to choose a disk, select your external hard drive. Follow the on-screen instructions to complete the installation.

Step 3: Set the External Drive as the Startup Disk

Open System Preferences

Go to the Apple menu and select System Preferences. Click on Startup Disk.

Select the External Drive

Click the external hard drive that now has macOS installed.

Restart Your Mac

Click Restart to boot from the external drive.

Additional Notes

Performance

Running macOS from an external drive may be slower than using an internal SSD, especially if the external drive is an HDD. Ensure that the drive is connected via USB 3.0 or Thunderbolt 3 for optimal performance.

Backup

Regularly back up your data on the external drive as it can be more vulnerable to disconnection or damage. Consider using Time Machine for convenient backups.

Power Supply

Ensure that the external hard drive has a sufficient power supply, especially for desktop drives. Some drives require wall power, while others can be powered by USB, which may limit performance.

Once you complete these steps, your Mac will boot from the external hard drive and you can use it as your main drive.

Conclusion

Converting an external hard drive into your main drive on a Mac is a useful technique for various reasons. Just follow the steps outlined in this guide to make the process seamless.