Time Machine Backup External Drive Title Image

The last thing you want as you’re happily editing that spreadsheet

Or ordering that pair of running shoes on-line.

Or showing your best friend that crazy holiday photo.

Is to get that fateful notice. The one that says you’ve a fatal error on your Mac’s internal drive.

And now you can’t access your Mac or your files.

Worried this could happen to you?

Your Mac might need a repair. Or you need to reinstall everything.

You can get both those things done. And get back all the stuff you have on your Mac.

Easily. As long as you have a backup.

Your recent Time Machine backup to an external drive means ….

If the worst happens to your Mac you can get all your files back. And be up and running pronto.

Because you’ve kept your files safe.

Learn How to Use Time Machine To Backup To Your External Drive

Before you start there are a few things to check on the external drive you’re using for your Time Machine backup.

Is it formatted in a way that Time Machine understands?

Don’t know how to check? Quickly read this document ‘ How To Check Format Of External Hard Drive On Mac‘ on the site.

Time Machine will only backup to an external drive if it’s formatted as HFS+.

You’ll see that your Mac calls this format Mac OS Extended (Journaled) file system.

And depending on the external drive you have you may need to format it first.

You can Learn how here.

Take 5 minutes to do that and head back here afterwards.

All set?


Now plug in your external backup drive and get yourself ready to backup with Time Machine.

Find Here The 7 Steps To Backup To Your External Drive With Time Machine

And setting up Time Machine for your external drive.

1. Start Up The Time Machine Software On Your Mac.

The easiest way to do this is to do a spotlight search.  Click on the spotlight search icon at the top of your Mac’s desktop screen.

Spotlight Search Symbol
Spotlight Search Symbol

Type in the words ‘system preferences’.

That searches your Mac for the system preferences program.  And on that screen you’ll see what you’re looking for – Time Machine.

Spotlight Search System Preferences
Spotlight Search System Preferences

2. Click On Time Machine.

Click on the Time Machine icon in System Preferences and your Mac’s Time Machine software starts up.

Now you’ll see your first Time Machine window.

Samsung T7 !st Time Machine Window
Samsung T7 !st Time Machine Window

On the left hand side of the screen under the Time Machine icon you’ll see a check box.  Check this box to choose to backup to your external drive whenever you plug your drive in.

On the bottom of your Time Machine window you’ll see another check box. This check box shows Time machine icon at the top of your Mac’s desktop, in your menu bar. It’s useful to put a check in this box.

You’ll find this useful if you want to check on how your backup is going.

Now, click the button on the darker right hand side of the screen ‘Select Backup Disk…’

3. Time Machine Select Backup Disk Window.

In this popup window you’ll find all the external drives physically plugged into your Mac. Plus the option to search for an Airport Time Capsule. But that’s a whole different story.

Pick on the name of your external drive. The drive you want Time Machine to backup to.

Look at the picture below

Samsung T7 Time Machine Choose Drive
Samsung T7 Time Machine Choose Drive

You’ll see the drive I’m using is called SamsungT7.

Yours will be called whatever you named it when you formatted it.

Click to picked your external backup drive for Time Machine. And you’ll see it highlighted in the list.

Then decide if you want to encrypt your backup.

There’s a check box at the bottom of this Time Machine pop up window.

If you decide to encrypt your backups. Then you’ll next see a prompt to put in a password.

Take care of this password. Record it somewhere safe. You’ll need it to get to your backup. And if you forget this password you’ve lost your backup.

4. Click ‘Use Disk’

And your Mac will now use your external drive to back up to.

Samsung T7 External Drive Picked
Samsung T7 External Drive Picked

You’ll notice some useful information just under your external drive’s name.

The size of your Time Machine backup external drive.

The oldest backup.

And the latest Backup.

And when your Mac is due to take the next backup.

And you find out here what Time machine keeps.

Time Machine keeps local snapshots when you have space.

It will take a backup each hour for the last 24 hours. Assuming your backup drive is connected and available.

Time Machine will keep a daily backup for a month.

And weekly backup until your backup drive runs out of space.

Then Time Machine deletes your oldest backup. This creates space on your external drive to make way for the latest backups.

It’s worth knowing something. That your Time Machine backup to your external drive is incremental forever. 

What does that mean?

Time machine backs up your changes. And when you’re ready to restore it recreates your Mac back to the time in point you’ve chosen from the backup.

5. Click On The ‘Options’ Button.

You won’t always need to do this but it’s worth knowing what’s there.

Samsung T7 Options Pop Up
Samsung T7 Options Pop Up

This Time Machine window allows you to exclude folders from your external drive’s backup.

You can click on the plus sign and add the folders you want to exclude.

Or check the box to exclude your Mac’s system files and your applications.

If you make no changes here then Time Machine will back up everything on your internal drive.

You’ll also see ready checked the box ‘Back up while on battery power’. This means that you’ll need to have your Mac plugged into external power to do your backup.

This is a good thing as the last thing you want is for your Mac to run out of battery power part way through your backup. Ruining your backup.

Click on the ‘Save’ button if you’ve made any changes or ‘Cancel’ if not.

6. Hurray You’ve Set Up Your Time Machine Backup To Your External Drive.

Your first Time Machine backup could take some time depending on how much you have to backup. And how fast your external backup drive is.

Backup’s after that will be much quicker. As only changes since the last backup will be backed up.

7. How To Check On The Progress Of Your Time Machine Backup.

When you checked the box to show the Time Machine at the top of your desktop this is how you use it.

Click on the Time Machine icon.

Samsung T7 Check Progress Of Time Machine Backup
Samsung T7 Check Progress Of Time Machine Backup

You’ll then see what Time Machine has already backed up to your external drive. And what is left to backup.

You can also click on this icon to find out when your backup is finished.

There are a couple of other ways.

Your drive icon on your desktop may turn green (depending on the version of Mac OS you’re running).

You may get a message telling you your Backup is Complete.

Samsung T7 Time Machine Backup Complete
Samsung T7 Time Machine Backup Complete

Remember To Eject When Your Backup Is Done

Your Mac holds all sorts of information in its memory while your drive is connected and backing up.

And it’s important that you plug out your external drive the right way so you won’t ruin your backup.

Samsung T7 Eject Drive
Samsung T7 Eject Drive

Right click on your drive’s Icon on your desktop. And pick Eject.

That way your Mac will write all that it needs from its memory to your external drive. When your external drive icon disappears from your desktop. And any activity light on your on your external drive goes out. Or keeps steady or whatever is appropriate for your external drive.

Then you can plug out your USB cable. And put your external drive safely away till the next time you want to backup.

Doing Your Next Time Machine Backup To Your External Drive

When you’re ready to do your next backup. Your Mac will remember the external drive you’ve chosen.

Plug it in. Plug in your Mac to external power. And that’s all you have to do.

Click on the Time Machine icon at the top of your desktop to check on the progress of your backup.

Be sure to Eject your drive properly when your backup is done.

To Backup An External Drive To An External Drive With Time Machine

Is easy to set up.

First have both drives plugged into your Mac.

2 External Drives Connected To Mac
2 External Drives Connected To Mac

They both should show up on your desktop. Though they may not show side to side like in the photo above.

If your Mac has only two USB C ports then you’ll need something to help.

Satechi On Desk

A USB C Hub Like The Satechi Aluminum Multiport Adaptor. Check The Write Up Here.

A USB hub allows you to plug your Mac into power and plug in more USB drives.

You can read an article on this site about it at the link above.

When you’ve both external drives connected to your Mac. Then walk your way through steps 1 through 4 above to pick the one you’re going to use as your backup drive.

At step 5 click on the ‘Options’ button.

Samsung T7 External Drive Pick Options
Samsung T7 External Drive Pick Options

Now you need to understand that your Mac automatically excludes external drives from your Time Machine backup. And that means you’re going to have to change that.

Time Machine 2 External Drives Options
Time Machine Option Window for 2 External Drives

When your second external drive is plugged in on the Time Machine options popup you’ll see your second external drive. The one you want backed up.

You’ll see in the photo the greyed out Samsung T7 drive (the one I am backing up to).

And the arrow in the photo shows a Seagate Desktop drive (the one I want to backup with Time Machine).

Now click on the drive you want Time Machine to backup.

Then click on the minus sign and take your second external drive off the excluded list. And then it’ll be included in the backup.

Yes, I know, it’s a little hard to wrap your head around it.

But your second drive was on the list of things excluded from your backup. Click on the drive and click minus. And now it’s included in the backup.

Now Time Machine will back up everything. Your Macs internal drives and the second external drive.


If you ONLY want the files of your external drive backed up by Time Machine. Then you’ll need to exclude the contents of your Mac.

On the options screen as well as clicking minus to take your external drive off the list.

You also click plus to include your Mac’s internal files on the excluded list.

By starting at the top level /.

Then you’ll be doing an external drive to drive backup using Time Machine.

When you’ve finished your changes click ‘Save’

Once set up your Mac will remember what you’ve set up. And the next time those drives are plugged in for backup It’ll be how you set it up.

At any time you can go into the Time Machine option screen and change it.

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