Have you ever thought of carrying your Mac OS on an external device and gain access to it at any time? If the reaction is yes, then you have arrived at the right post. We will be providing you with the information through which you can install macOS High Sierra on an external drive.

1. External Hard Drive For Macos High Sierra

Dec 12, 2017 Home Mac Recovery How to Fix Mac Not Detecting External Hard Drive in Sierra or High Sierra Summary: There are several reasons why your Mac won’t recognize external hard drive. If you are experiencing external hard drive not mounting in macOS Sierra or High Sierra, read on this post to get potential solutions to this problem.

Part 1. How to Install macOS High Sierra on the External Drive

How to Use macOS High Sierra with the Bootable Hard Drive As you now have macOS High Sierra in the form of bootable hard drive, you can use it with another compatible Mac or when the situation demands. However, remember that using the external device as a bootable drive will slow down the functioning of the system. As the best free Mac data recovery, iBoysoft Data Recovery for Mac is able to recover lost data from unmountable, unreadable, corrupted, inaccessible external hard drive, hard drive, USB flash drive, SD card, memory card, etc. It supports to recover documents, photos, music files, videos, emails on macOS Catalina 10.15/Mojave 10.14/High Sierra.

Before beginning the process, there are a few requisites that you must meet. You will need an external drive with a minimum capacity of 16 GB, and second, you will need the copy of the macOS High Sierra installer. You can obtain the installer from the App Store by searching for 'macOS' and download it to your Mac hard drive.

Step 1: Formatting the External Drive

To allow the external drive to function as the startup disk, you need to format it to Mac OS Extended and employ GUID partition map. Start the utility disk. You can find it under the Applications category or search it using Spotlight.

As utility disk runs in the background, you can check for the format of the external drive. In the following example, the drive is in Master Boot Record format. First, unmount the drive. After unmounting, you can select the same drive from the left of the window as shown in the figure below. Now, from the tabs that appear in right window, choose 'Erase' option.

In the next window, you can now format the external drive as 'Mac OS Extended' and opt for GUID Partition Map. If you choose to, you can also give it a name. Press 'Erase' to proceed. After completion, you will see the following screen. Press 'Done' to proceed.

Step 2: Installing macOS High Sierra on the External Drive

After you complete the download of the macOS installer, double click the same from the Applications folder to begin the installation procedure. Press 'Continue' in the following screen.

Click 'Agree' to the accept license agreement. In the next window, press the 'Show all disks' option. The window will display the local drive and the connected external drive. Choose the external drive in this case. You will have to key in your system user name and password.

macOS High Sierra will begin installing on the selected external hard disk. It requires some time to complete the task. You can wait until the process is complete. Before it completes the installation, the Mac will restart. Therefore, it is preferable to save any other work that is in progress.

After restarting, the Mac will take a minimum of 15 minutes to complete the installation process. It will then reboot from the new device. You then have to proceed with the general process of activating Siri, time zone, and adding the user account. Once you complete these actions, you will possess the new version of macOS High Sierra on your external drive. Do not remove the external drive, as Mac OS will access the files on the drive periodically. You can now use the same every time you wish to use High Sierra.

Part 2. How to Use macOS High Sierra with the Bootable Hard Drive

As you now have macOS High Sierra in the form of bootable hard drive, you can use it with another compatible Mac or when the situation demands. However, remember that using the external device as a bootable drive will slow down the functioning of the system. More importantly, it is useful only when you are facing trouble with your existing internal drive of the Mac.

The following information will be helpful in case if you choose to use macOS High Sierra with the bootable hard drive:

Step 1: If there is a trouble with the current hard disk, and you wish to solve it or use the new version of the OS, then plug the bootable external drive to the Mac.

Step 2: Power on the machine and hold the option button until you notice the recovery screen appear. From the screen, you can choose the bootable external device that you have created.

Step 3: You will boot into the macOS High Sierra version for that particular session.

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Related Articles & Tips

Erasing your disk: For most reasons to erase, including when reformatting a disk or selling, giving away, or trading in your Mac, you should erase your entire disk.

Erasing a volume on your disk: In other cases, such as when your disk contains multiple volumes (or partitions) and you don't want to erase them all, you can erase specific volumes on the disk.

Erasing a disk or volume permanently deletes all of its files. Before continuing, make sure that you have a backup of any files that you want to keep.

How to erase your disk

1. Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue.
   If you're not erasing the disk your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.
   
2. Choose View > Show All Devices from the menu bar in Disk Utility. The sidebar now shows your disks (devices) and any containers and volumes within them. The disk your Mac started up from is at the top of the list. In this example, Apple SSD is the startup disk:
   
3. Select the disk that you want to erase. Don't see your disk?
4. Click Erase, then complete these items:
   • Name: Type the name that you want the disk to have after you erase it.
   • Format: Choose APFS or Mac OS Extended (Journaled). Disk Utility shows a compatible format by default.
   • Scheme: Choose GUID Partition Map.
5. Click Erase to begin erasing your disk and every container and volume within it. You might be asked to enter your Apple ID. Forgot your Apple ID?
6. When done, quit Disk Utility.
7. If you want your Mac to be able to start up from the disk you erased, reinstall macOS on the disk.

How to erase a volume on your disk

1. Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue.
   If you're not erasing the volume your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.
2. In the sidebar of Disk Utility, select the volume that you want to erase. The volume your Mac started up from is named Macintosh HD, unless you changed its name. Don't see your volume?
3. Click Erase, then complete these items:
   • Name: Type the name that you want the volume to have after you erase it.
   • Format: Choose APFS or Mac OS Extended (Journaled). Disk Utility shows a compatible format by default.
4. If you see an Erase Volume Group button, the volume you selected is part of a volume group. In that case, you should erase the volume group. Otherwise, click Erase to erase just the selected volume. You might be asked to enter your Apple ID. Forgot your Apple ID?
   
5. When done, quit Disk Utility.
6. If you want your Mac to be able to start up from the volume you erased, reinstall macOS on that volume.

Reasons to erase

You can erase at any time, including in circumstances such as these:

• You want to permanently erase all content from your Mac and restore it to factory settings. This is one of the final steps before selling, giving away, or trading in your Mac.
• You're changing the format of a disk, such as from a PC format (FAT, ExFAT, or NTFS) to a Mac format (APFS or Mac OS Extended).
• You received a message that your disk isn't readable by this computer.
• You're trying to resolve a disk issue that Disk Utility can't repair.
• The macOS installer doesn't see your disk or can't install on it. For example, the installer might say that your disk isn't formatted correctly, isn't using a GUID partition scheme, contains a newer version of the operating system, or can't be used to start up your computer.
• The macOS installer says that you may not install to this volume because it is part of an Apple RAID.

About APFS and Mac OS Extended

Disk Utility in macOS High Sierra or later can erase using either the newer APFS (Apple File System) format or the older Mac OS Extended format, and it automatically chooses a compatible format for you.

How to choose between APFS and Mac OS Extended

Disk Utility tries to detect the type of storage and show the appropriate format in the Format menu. If it can't, it chooses Mac OS Extended, which works with all versions of macOS. If you want to change the format, answer these questions:

• Are you formatting the disk that came built into your Mac?
  If the built-in disk came APFS-formatted, Disk Utility suggests APFS. Don't change it to Mac OS Extended.
• Are you about to install macOS High Sierra or later for the first time on the disk?
  If you need to erase your disk before installing High Sierra or later for the first time on that disk, choose Mac OS Extended (Journaled). During installation, the macOS installer decides whether to automatically convert to APFS—without erasing your files.
• Are you preparing a Time Machine backup disk or bootable installer?
  Choose Mac OS Extended (Journaled) for any disk that you plan to use as a Time Machine backup disk or as a bootable installer.
• Will you be using the disk with another Mac?
  If the other Mac isn't using macOS High Sierra or later, choose Mac OS Extended (Journaled). Earlier versions of macOS don't work with APFS-formatted volumes.

How to identify the format currently in use

Virtualbox for mac os high sierra. If you want to know which format is currently in use, use any of these methods:

External Hard Drive For Macos High Sierra

• Select the volume in the Disk Utility sidebar, then check the information shown on the right. For more detail, choose File > Get Info from the Disk Utility menu bar.
• Open System Information and select Storage in the sidebar. The File System column on the right shows the format of each volume.
• Select the volume in the Finder, then choose File > Get Info from the menu bar. The Get Info window shows the Format of that volume.

If your disk or volume doesn't appear, or the erase fails

1. Shut down your Mac, then unplug all nonessential devices from your Mac.
2. If you're erasing an external drive, make sure that it's connected directly to your Mac using a cable that you know is good. Then turn the drive off and back on.
3. If your disk or volume still doesn't appear in Disk Utility, or Disk Utility reports that the erase process failed, your disk or Mac might need service. If you need help, please contact Apple Support.

Learn more

• If you can't start up from macOS Recovery, you can use a different startup disk instead.
• If Disk Utility shows a Security Options button in the Erase window, you can click that button to choose between a faster (but less secure) erase and a slower (but more secure) erase. Some older versions of Disk Utility offer the option to zero all data instead. These secure-erase options aren't offered or needed for solid-state drives (SSDs) and flash storage.