How To Choose an External hard drive for Backup On A Mac

When you haven’t a Clue

You need an External drive for a backup but Macs are special. You need to find the right type of drive. A drive that will work on your Mac. So the question is really how do you choose the right kind of external drive to back up your Mac?

The key is to understand what you need so you can get to the bottom of

Your specific wants and needs before you check out the choices.

How best to do that? Stick with me to find out.

Best Place to Start when you haven’t a Clue

When You Haven't a Clue

Is to understand what you have;

In particular, what internal drives do you have on your Mac, and what physical ports –

ports are the places where you physically plug the hard drive into.


By knowing what internal drives you have tells you a lot about your range of choices.

Find out by clicking on the Apple symbol, top right of your desktop screen and select about this Mac.

About This Mac Screen
About This Mac

Across the top of the about this Mac window you have the buttons :

Overview, Displays, Storage, Memory, Support, Service

System Report Choose Storage
System Report Choose Storage

Click on the Storage button.

The next screen will tell you the amount of drive space Gigabytes (GB) available and the size of your drive.

In the example below the Mac has a 250 GB internal drive of which 136 GB is used (hint round up the numbers) and you can also see that this particular Mac has an eSata drive on it, yours could be an SSD – Solid State Drive.

System Report Storage
System Report Storage

Make a note of what is on your Mac. As the amount of drive space used equals the files and documents you will want to backup.

You can dismiss the window by clicking on the small red button top left.

The very newest Macbook Pro’s can be bought with up to 2TB of SSD internally, and the newest Macbook Air’s with up to 512 GB of SSD.

SSDs are Solid State Disks drives and they are fast.

Understand what is on your Mac and how much you are currently using.

One Mac or Several

If your plan is to backup several Mac’s then do the same with each Mac. Find out what type of drives they have. The total drive size and what is currently being used.

What Interfaces are On Your Mac

The next thing to find out is, what ports you have and if you haven’t a clue. Then it’s back to About your Mac, as above. This time when you get to the About your Mac screen, click on the system report button.

Choose System Report
Choose System Report

You’ll be able to select the Firewire, USB, Thunderbolt and Wifi options in turn and make a note of what you have. Firewire 400 or 800? USB 2.0 or 3.0 or 3.1. What does it say under Thunderbolt? What does it say under Wifi?

Find Out What You have on Your Mac
Find Out What You have on Your Mac

If you have an 802.11ac interface then you have a more modern Mac and fast Wifi.

Why is this all relevant?

Because it tells you what kind of external drive could be best for backup and your options for connecting those drives. Make a note.

You can dismiss the window by clicking on the small red button top left.

Internal Disk Drives versus External

What the difference is and why it’s important?

I would just like to take a minute to explain the whole internal versus external thing just in case you think, wow I have so much free space, I’ll just backup to my internal hard drive.

Why you typically do not backup to an internal drive

A backup is your plan B or C depending on whether you have other places you keep copies of your data.

It’s there in case the worst happens and you loose your Mac’s internal drive. If your backup, your insurance policy is on that same internal drive and you’ve had a drive crash then all your data is gone … Including your backup.

It is far better to keep your backup physically separately, on a hard drive that is external to your Mac – hence the term external drive.

You can then, if the absolute worst happens restore your backup to a brand new Mac. There would be no way to do that if your backup was on your internal drives. So now that’s all cleared up let’s talk options.

Interfaces USB, USB C, Thunderbolt, Firewire, Wifi

External drives are sold in a variety of capacities – storage sizes and with a range of interfaces.

So let’s talk a bit about those interfaces.

USB, USB C and Thunderbolt

USB is the most popular interface. And here are the available options along with the theoretical speed of the interface.

USB VersionSpeed
USB 2.0480 Mbit/s
USB 3.05 Gbits/s
USB 3.1 Gen 15 Gbits/s
USB 3.1 Gen 210 Gbits/s

It is important to note that these are theoretical maximum speeds that the interface and the drive could communicates at – ship your data back and forth, but there are overheads which mean that these speeds can be reduced in practice by 20 to 30 percent.

What USB interface you have on your Mac tells you largely what USB options you have. What does that mean?

Let’s talk through an example:-

Say you have USB 3.1 port on your Mac, then you could put a USB 3.1 external hard drive on and match the speed to what you have on your Mac.

USB is also backwards compatible thank goodness.

So you could put a USB 3.0 external drive on (it’s unlikely you would get a USB 2.0 external hard drive these days). Because of backwards compatibility your Mac would talk to the slower external hard drive at the speed the slower drive is capable of.

Why would you do this?

Well USB 3.0 external hard drives are cheaper than USB 3.1 drives, and if you are only needing the drive for backup and if ultimate speed is not the issue – because you have the time to do your backup, then why not.

One more thing to be aware of is that the physical connections changed on Mac’s between USB 3.0 and USB 3.1.

So in the example above you’d also need an USB adaptor cable – a USB 3.0 to USB 3.1/USB C adaptor cable. Easy bought on Amazon and for the cost saving again why not.

Thunderbolt is also a USB based interface.

Thunderbolt Gen 1 which is equivalent to USB 3.1 Gen 1 and

Thunderbolt Gen 2 which is equivalent to USB 3.1 Gen 2

and the physical interface on the Mac for Thunderbolt is also referred to as USB C.


Macs also had Firewire ports – Firewire 400 and Firewire 800. Both interfaces are backwards compatible similar to USB.

They operated at 400 Mbits/s for Firewire 400 and 800 Mbits/s for Firewire 800.

Those Apple native ports were pretty fast, faster than USB 2.0 because they operated at closer to their native speeds because of lower overheads.

And allowed you to connect in other peripherals other than hard drives.

If you have Firewire ports on your Mac you may want to consider purchasing an external hard drive with Firewire connections particularly for an older Mac where your other option could be a drive connected via a slower USB 2.0 port.

Connect an External Drive Over Wifi


If you have a decently performing Wifi interface on your Mac, – 802.11ac then you could consider getting a networked attached external hard drive …

A drive with Wifi connectivity. The Apple Time capsule is a good example of a networked drive device that would allow you to backup over Wifi whenever your Mac is in Wifi range of the Time Capsule. Then you wouldn’t have to think about remembering to connect in your external drive for backup as it would be all taken care of for you.

If you want to find out more about the Apple Time Capsule I have an article on it.

How much Drive Space do you actually need?

Now that we have explored the interfaces available, lets talk capacity.

Remember earlier I asked you to find out how much drive space you have and how much drive space your actually using. Now is the time to use that information.

If you have a 500 GB internal drive, it would be best to get a 1TB external drive for backup. Even if you are only actually using half.

If you plan on backing up multiple Mac’s then either

Get an external hard drive for each that is double the internal hard drive capacity


total up the storage space you need and get one larger drive and be prepared to partition up that drive so that you can backup multiple Mac’s.

I have an article on the site that tells you how to partition up a drive – in that instance for Mac and PC’s but the principal is exactly the same and it only takes a few minutes.

How Often will you Perform Backups?

This is important to understand because an external drive that is used once a week or so for a backup

compared to one that is constantly plugged in and on

are under very different strains.

One will be backing up on a hourly basis, and on all the time and the other will be on only when it is backing up.

Why does that matter? Because there are …

Different Types of Hard Drives

I’m really talking about low cost, versus more expensive and higher quality. So lets understand what is out there.


The portable drives have laptop quality drives in them, which are mechanically based.

Inside of Mechanical Hard Drive
Inside of Mechanical Hard Drive

This means that they have moving parts in them which mean they are more susceptible to knocks and bangs. Are lighter and more convenient but lower in quality. If used everyday then you can expect this drive to last typically for about two years.

They are lower cost, the WD Elements, Toshiba Canvio Advance and the Seagate Expansion are all examples of this type of portable basic drive.

If you are using for a once a week plug in and backup then they could be a great option.


These drives are also mechanically based. Typically faster, better quality and designed more for daily use and they make a great backup option. They are used on a solid surface, hence the term desktop, and are not generally portable.

They are not designed to be portable but there is no reason you couldn’t take one with you as long as it was in a good carry case. They are that bit larger.

You should see a drive like this last you three years or more. The G Drive USB 3.0 is a good example of this type of drive.

Solid State Drives

These are electronically based, so much more suited to being ported around. They are top of the range, the fastest drives and the more expensive option. A 1TB SSD drive is significantly more expensive than a 1TB hard drive.

But you will get delightfully fast backups and if speed is more important to you than cash, they are a great option. The Samsung T5 is a great example of a portable SSD.

And if you need to take your drive out to inhospitable environments then the LaCie Rugged SSD external drive may just be for you. Or for a non SSD drive the Transcend Military Drop Tested drive.

Ok so what does this really mean?

What Does this Mean?

You can mix and match. Just because you have an SSD drive internally on your Mac, doesn’t mean you have to put on an SSD external hard drive for backup. In fact it may be overkill, especially if you’re price sensitive and speed of backup isn’t crucial.

With an USB adaptor cable you could use an USB 3.0 basic drive or desktop drive if that was more cost effective.

At the other end of the spectrum, if you have a USB 2.0 port on your Mac, it makes little sense buying SSD drives, unless you want it for other features such as it’s robustness.

Your Mac will be unable to ship the data out to the external hard drive at anywhere near the speed the SSD is capable of, so unless there is another reason,

You may as well go for a USB 3.0 based drive. The speed will be down shifted to match your Mac and your pocket may be a little happier.

Type of File Systems

When you purchase an external drive the drive will come preformatted – with something called a file system on it.

It may come formatted to FAT32, ExFAT or HFS+.

For a Mac user this is of small concern because I would recommend you reformat – put a new file system on the external drive anyway.

It’s quick and easy to do and means you can choose virtually any drive for your Mac. There is an article on the site that covers how to do this.

Let’s talk Backup Software

It’s time to discuss the software you’ll be actually using to backup with. On a Mac your backup software will almost certainly be Time Machine and it is

included in Mac OS.

What Time Machine Needs

  1. A connected external drive,
  2. Of sufficient size,
  3. Formatted to Mac OS Extended (Journaled) file system (HFS+)
    You can learn, how to format an external drive here.
  4. Time Machine needs to be told to use that external drive as its backup drive. You can learn how to do that here.

Understanding how Time Machine Works

On the first pass Time Machine will take a backup of the used space of your internal drive. The first backup is also known as a full backup and it can take a little while. After that, all the Time Machine backups are;

Incremental forever.

That means that when the backup drive is plugged in, Time Machine will backup everything that has changed since the last backup.

And then if the backup drive remains connected, backup up once an hour for the next 24 hours, then Time Machine keeps daily backups for a month, then weekly after that.

Until you disconnect the external drive.

On reconnecting the drive, Time Machine then will backup everything that has changed since the last backup.

When the backup drive is full Time Machine deletes the oldest backup and carries on incremental forever.

Remember earlier when I said that you should get an external drive twice the size of your internal drive. It is for this reason. You can grow into the space available on your new drive without being worried about the oldest backup being deleted …

Until it becomes irrelevant.

Getting your Files Back

When you need to restore you can restore your entire drive. Or

Go back in time and restore a single file from a few months or even years ago.

In Conclusion

Choosing an external drive for backup on your Mac is easy even if you haven’t a clue.

Because you’re going to;

  • Understand what you have on your Mac, interfaces, size of drive and type of drive.
  • This will tell you the types of external drives you can get. – interface, size and type. Remember backwards compatibility.
  • Decide how you want to backup, physical connection via USB, Firewire or over Wifi. Where you’ll be backing up, in an office or on the go. How often. Continually or once a week, as this will dictate the quality of external drive you should consider.

Armed with these three things makes the choice straight forward, because you now have a much better understanding of what you need.

You can check out some of the best external drive options here on the site

Other Questions

Do any external drives Work With a Mac?

Essentially yes, because Mac OS will see the drives, and you can reformat them to a file system Mac OS is happy with. So you can use any drive.

The exception may be with older Mac’s with USB 2.0 ports, and the newer portable drives powered from the USB port. Care needs to be taken that the portable drive does not demand more power to work than the port on the Mac can supply. Unless it is easy for you to check and be happy that others have used that brand of portable on your Mac, I would stick with a drive with a separate power adaptor.