Clone Your Mac Boot Drive to an External Drive 12 Steps

By Simon Irons / September 2, 2018
Clone Mac Boot Drive

It's a great idea to have a clone copy of your Mac's internal hard drive - a Mac boot clone drive - just in case your hard drive fails.

You then have the option to get yourself up and running on your Mac with all your files by booting from your cloned drive.

And you will need to take a clone of your Mac's boot drive if you plan on upgrading your internal disk to an SSD or larger capacity hard drive.



Who is This Article For?

My article is written for those who want a simple way, using software available on their Mac to create a bootable copy, also known as a clone of their Mac's internal drive to an external drive.

Why Clone Your Mac Bootable Drive?

​1. It allows you to have an external hard drive that is a copy of your internal drive that you can boot from should the worst happens and your Mac's internal drive fails.

2. It is a way of cloning your internal drive to an external drive should it be a hard drive or SSD (Solid State Drive) that you plan to replace your internal drive with. At the end of the process you have an exact copy, bootable, should you want to replace an older slower internal drive with a newer, faster hard drive or SSD. Or indeed replace with a drive with more capacity.

3. You can create a copy of your internal drive ahead of any major operating system update. Because should the update fail or cause problems with your Mac or a piece of crucial software you are using on your Mac, you can always revert back - because your clone is an exact copy of your Mac before the upgrade.

What Will You Get?

​I show you how to clone and create a bootable copy onto an external hard drive by using freely available software on your Mac - MacOS Utilities and Disk Utility.

All you need is knowledge (I tell you how here) and an external drive large enough to create your bootable clone onto.

What you are going to need

​An external drive be it a hard drive or SSD (solid state drive). Cloning will erase everything on the new drive, replacing it with the contents of your internal Mac's boot drive, so copy anything you want off the drive first.

The same as cloning an external drive to another external drive, the drive you want to clone onto - your new, empty drive must be already formatted to Mac OS Extended (Journaled) file system, with the scheme chosen as GUID Partition Map. ​

It must be of the right size, if you have a 250 GB internal drive then the external needs to be at least 250GB preferably larger.

Your Mac's internal drive (the drive to be cloned) and the clone (the external drive) can't be in use while the cloning happens.

The beauty of using MacOS Utilities and Disk Utility is that both drives are unmounted allowing you to take the boot clone.

Take a Time Machine backup of your Mac's internal hard drive before you start, just in case things don't go quite to plan. ​

Overview of What You Will Be Doing

  • ​You will boot your Mac into Recovery mode.
  • Use MacOS Utilities and Disk Utility to format the external hard drive.
  • Name the external drive to match exactly your Mac's internal drive (don't do this ahead of time).
  • Then carry out the cloning, which Disk Utility calls Restore

To Create the Bootable Clone on the External Hard Drive the 12 Steps

1. Start with your Mac powered on and connected to external power - you don't want your battery running out part way through the process. You want the external hard drive (or indeed external SSD) plugged into your Mac.

2. Next you need to reboot your Mac into recovery mode.

Go to the top of the screen and select Restart (or Shutdown and then power on).

Restart Mac

Restart Mac

​3. While your Mac is booting up, hold down the command key and the letter r.

You'll hear the chime. You can release the keys once you see the Apple logo.

Boot To Apple Logo

Boot To Apple Logo

​4. Now wait until you see the MacOS Utilities screen.

You may see a screen ahead of MacOS Utilities where your Mac asks you to select the language you are using.

Boot Select Language Screen

Boot Select Language Screen

Select the language and the MacOS Utilities screen will be next.

​Note

Should you at any stage before starting the cloning process want to Exit and not continue, you can by moving your cursor to the top of the screen.

Click on the Apple logo, select shut down and then you can restart normally.

Not seeing the Apple logo at the top of the screen?

Move your cursor there anyway and it will appear.

MacOs Utilities Select Disk Utility

MacOs Utilities Select Disk Utility

5. Select Disk Utilities from the menu.

You will then see a list of all the drives connected to your Mac.

List of all the drives

List of all the drives

​On the left hand side of the screen you'll see under the heading Internal, your Mac's internal drive or indeed drives if you have more than one.

Under the heading External, you'll see listed your external drive.

6. Select your external drive the new, clear drive you want to clone onto.

Disk Utility Select Erase

Disk Utility Select Erase

​Be sure to select the drive at the right level. The yellow arrow in the above picture shows you where. Next select Erase from the top of the Disk Utilities screen. The yellow circle shows where.

Now you perform a format of the external drive.

7. On the next menu you want to leave the drive name as untitled, the next two options are very important.

Disk Utility Choose MacOS Extended

Disk Utility Choose MacOS Extended

​You want the format to be Mac OS Extended (Journaled). Select that from the drop down list

and the scheme to be GUID Partition Map,

Disk Utility Choose GUID

Disk Utility Choose GUID

​You want what you see on your screen to match the picture above.

Then click on the Erase button.

Disk Utility Click Erase

Disk Utility Click Erase

​In a few minutes the external drive will be reformatted.

Once the hard drive has been formatted click on done

Confirm Erase Done

Confirm Erase Done

​8. The external drive has been formatted the way you need and named as 'untitled' and now you change the name.

Change Name to Match Internal Drive

Change Name to Match Internal Drive

​Click at the second level of the external drive (the yellow arrow in the above image shows you what I mean by the second level)

and then on the name untitled in the center of the window.

You are now ready to change the external hard drive's name to match the name of your Mac's internal drive.

Your internal drive's name is on the second level of the internal drive list.

Name Changed To Match Internal Boot Drive

Name Changed To Match Internal Boot Drive

​The yellow arrows illustrates what I mean. In this example the internal drive is called 'Macintosh HD'

Type in the new name onto the external drive so it is exactly the same as your internal bootable drive. Following any capitalization and spacing.

Press enter when you have finished typing in the name.

9. Now you are ready to start the cloning process.

Your external hard drive should still be selected. Move your cursor to the top of your screen and select the edit menu and from that menu select restore. This is what Disk Utility calls the cloning/copying process.

Select Edit Restore

Select Edit Restore

​10. The next window asks you to select the drive you want to restored onto your empty external drive. Select your Mac's internal drive from the drop down menu.

Select To Restore from Internal Drive

Select To Restore from Internal Drive

​11. Click on the Restore button.

Select to Start Restore

Select to Start Restore

​Wait, as this restore is going to take a while depending on how fast the external drive is and how big your internal drive is.

Once done, Click Done.

You have your bootable clone.

12. Head to the top of your screen, click on the Apple logo and select shut down to exit MacOS Utilities and reboot as normal from your Mac's internal drive.

YouTube Video

​I have found a YouTube video that you can use as an additional resource should you want to watch a video as well as following my instructions.

I think you should find this near sixteen minute video useful and he also shows you how to use the new external drive as a destination for Time Machine once you have created it as a bootable clone.

A couple of things I would say before you decide to do that. The external hard drive has to have enough capacity to hold your boot clone (so at least as big as the drive you are cloning) and probably twice the size, as you will need room to take your Time Machine backups and grow into it over time.

The other thing I would say is personally I like my clone boot disks separate from my Time Machine backups. Because should that disk fail you have lost your clone and your Time Machine backups all in one.

All that said it is a great video, with just the one caveat I have.

Clone Bootable Apple Mac Hard Drive from Disk Utility Mac OS Sierra 2017

Video Credit: AVME Videos

To Boot From Your New Bootable Drive

1. Non Emergency

​​In a non emergency controlled situation when your Mac is able to be booted normally from its internal drive you can select to boot from the external drive.

Start up your Mac normally, connect the external drive

Start up system preferences

You can find System Preferences either from your Applications folder or use spotlight search (found at the top of your desktop window).

Spotlight Search Symbol

Spotlight Search Symbol

​and type in System Preferences

Spotlight Search System Preferences

Spotlight Search System Preferences

​And click to start it up from there.

Once in System Preferences click on Startup Disk

System Preferences Startup Disk

System Preferences Startup Disk

​The next screen will show you all your available and connected boot drives. Your Mac's internal drive and the external boot drive you created.

Available Boot Drives

Available Boot Drives

​Your internal drive is the drive you are currently booted from and is shown in grey, your external drive is shown in yellow. Click on that and then select restart.

Set Restart From External Drive

Set Restart From External Drive

​If you have the lock on to prevent changes in System Preferences, you will need to unlock and type in your main password.

Then you have changed the default drive your Mac starts from to the external drive.

2. In An Emergency

​When you don't have access to your internal drive to boot normally.

Start up your Mac and hold down the option key.

Your Mac will then present you with the start up manager screen that allows you to choose the drive you want to boot from. ​

Select the external drive and your Mac will boot from that.

FAQ

​Q. I have a 1TB internal drive but used only 250GB and the external SSD I have is 500GB. Can I use this method to clone onto the external SSD?

A. With this method you need the external drive to be least as big as the internal drive. As the internal drive is 1TB and your external SSD is 500GB you won't be able to use this method.

Despite the fact that you are only using 250GB of the internal drive.  This is because Using Disk Utility to clone in this way is a block by block copy, this method does not differentiate between used space and empty space. It is an exact copy of one drive to another. You would need to use a different method.

Q. My Mac's internal hard drive has failed and I now need to boot from the external drive to carry out repairs.

A. Take a look at the section above To Boot from your now bootable drive, point 2, In an emergency. Restarting your Mac while holding down the option key will allow you to choose the external drive to boot from.

Last Words

​Now you have the knowledge of how to clone your Mac's bootable drive.

I hope you enjoyed my article - should you want to take a backup of an external hard drive to another external hard drive, I have an article that has you covered.​

And related to this article should you want to clone an external hard drive to another external hard drive I have another article showing you how.

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