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Boot Backup Drive

UPDATE: September 2023

As mentioned on the Chronosync Help pages. Apple has made it increasingly difficult to create a fully bootable backup drive. So the solution to creating a backup copy of your boot drive has changed. Take a read of this guide on their website


The Theory

I realised a few years ago now, when sitting thinking about backup of my computer and images, what about the boot drive? It’s all well and good having a backup of your data via TimeMachine or other. But have you ever tried restoring that data? It’s darn slow.

What would happen if the drive inside my main computer (iMac) died? One of the things about an iMac is you can’t just open it up and remove the drive. But not only that, even if you could remove it – what then?

The solution I came up back then and still use to this day is a Bootable Backup drive. One drive, dedicated to being a 100% copy of my boot drive. That has the ability to boot from it! So if the main drive died, you can simply restart, but press down the option key on the Mac and it will allow you to boot from the Boot Backup drive. You’d be up and running within minutes.

So every night my computer runs an automated script (using Chronosync) that copies over my main hard drive to the Boot Backup drive. It’s a 100% mirrored copy. Any files that have changed since the previous night are put into a folder called Archive.

Chronosync Bootable Backup Settings

This is not strictly a Backup Drive (yeah, I know, the terminology could be better). But by definition a backup would be a copy of the original data, with incremental copies too. This will do that to a certain point, as there is the Archive folder. But due to the drive being small (the same size as the boot drive) at some point, those archived files will fill up the drive.

I will normally delete the Archive folder as soon as it hits its limit. You’ll know that’s happened as the auto backup will send you a message saying backup failed, drive full.

If cost were no option, one could of course have a Boot Backup drive that was way bigger than the internal boot drive. But that would be very expensive. Example, I can get a 1Tb external SSD for around £120-140, but a 2Tb version would be over £220 at time of writing.

UPDATE – so I’ve just had to do this all myself. As I have just bought a brand new Samsung T7 as my backup drive. I ended up trying the Bootable Assistant method linked below. It works like a treat. Very easy to follow, though it probably helps that I understand the theory and have done it before. But it’s pretty neat how it can even format the drive for you. The T7 arrived with some random files on it. I wiped it, don’t need it. It’s still worth reading through the rest of this article, so you fully understand what it’s doing.

How to Create a Boot Backup Drive

Items needed:

1/ A hard drive of at least the same size as your main boot drive. Mine is 1Tb. Ideally, this needs to be a fast drive. More on this later, but I tried booting from a USB3 hard drive and it works, but is painful. An SSD would be a far better choice. My ideal drive would be a small portable SSD unit. That way, if I had to take it somewhere – to plug into someone else’s computer for instance, it would be easy to do. No power leads to worry about.

2/ Chronosync – My favourite backup software, file copy software for the Mac. I’ve used it for many years and it’s simply bullet proof. It’s always kept up to date with software releases and has many options from simply copying files from one drive to another up to doing a full hard drive copy with the ability to boot from the drive. Worth every penny.

That’s it – drive could be Thunderbolt or USB3. The old USB2 would be far too slow. Thunderbolt drives tend to be far more expensive than USB3. But if you have an old one lying around, it’s a great connection type.

NB: If you are using the new Big Sur OS, then the procedure below will not work. You need to follow the instructions given on Chronosync’s help page.


For OX Catalina and older you can either follow Chronosync’s own guide here or follow my own steps below. Or you can take advantage of their Bootable Backup Assistant option. They all do essentially the same thing. The backup assistant method was actually quite easy to follow.

1/ Plug in your external hard drive. It needs to be formatted to the same type of format as your main hard drive (the one you’re backing up). You can do this using Disk Utility – in the Utilities folder of your Applications folder. Or alternatively you can allow Chronosync to do this for you. If it’s not set correctly, then Chronosync will warn you that it’s not set – and will offer to fix it for you.

3/ Rename your new Boot Backup Drive to a sensible name. I generally call it Boot Backup. But any name will do, that you can identify it. I’m currently using a temporary drive and have called it Boot Samsung 2Tb, so I know which one it is.

2/ Open Chronosync and click File, New Sychronizer. This will bring up the window shown below

Chronosync Main Window

Before proceeding, I always like to set up Chronosync so it always defaults to my favourite settings. These are shown below. They may be slightly different from the default settings. Which I seem to remember don’t have Verify Copied Data set by default. Which I think is essential. It checks every file copied using by comparing it to the original. I always have this ticked. There’s no way you can manually check through thousands of files to see if they are the same. This method is infallible. I use this all the time to copy over photos from one drive to another with absolute certainty that the copy is accurate, without ever having to open up the files to check.

Chronosync Options Window

Now, we’re ready to do our first copy. This will obviously be a slow process, as it has to copy over the whole of your root hard drive. Be patient. Subsequent backups will be far faster, as they will only be copying over file changes made per day. And that subsequent backup can be set to run automatically every day.

For the first run, you could choose Bootable Left to Right – or – Bootable Mirror Left to Right. They will essentially do the same thing on the 1st run. As you are simply trying to copy all of the data on the left hand drive (your root drive – your main hard drive) to the new drive on the right hand side.

To get the drives in the right place in the Chronosync window, you simply drag them from the Finder to this window. They should appear as below.

IMPORTANT – check the drive on the right hand side is the correct one. Because when you hit Synchronise, it’s going to start overwriting that drive…. Be careful, no need to rush this stuff.

Chronosync Bootable Backup Settings

While running, you will see a screen similar to the one below, with all the files being copied, flashing up on screen.

Chronosync Running

After a few hours. The Boot copy should finish. Chronosync will tell you it’s finished and on the final screen it will show you information about any files that might have been skipped or any errors encountered. If there are any of either, you can always re-run the sync again – using the Mirrored setting. It will simply scan both drives and try again to copy over the missing files. Running this multiple times will not hurt anything. Ideally, you should have no errors and no skipped files.

Chronosync Complete Screen

Booting Up from your External Drive

Restart your Mac, then press and hold down the Options Key on your keyboard. Full Apple Guide here – including a note about the T2 security chip in modern Macs. Which you need to setup properly to allow rebooting from external drives.

This should work fine on a wired or wireless keyboard. However, if it doesn’t, then it’s advised to reset the PRAM following this guide

Which Drive to Buy?

For many years, I’ve been using a Lacie 1Tb RAID as my Boot Backup drive. It was superb. Two SSD’s as a RAID made it very fast. However, recently Apple in their wisdom decided to remove the ability to boot a Mac from a RAID. So the drive has become unworkable for this task.

So, I had to find a new drive. I had an old 2Tb Maxtor portable drive lying on my desk. Which I used to use as my TimeMachine drive. My TimeMachine now runs on a 5Tb portable drive, so that it’s got lots of room for growth. So I tried using the 2Tb as a boot backup. Its a USB3 drive. However, it’s a tiny hard drive probably running at only 5400rpm. The iMac booted up just fine. But it took AGES…..

Everything works. But it’s like working in glue. So ridiculously slow to start up, to start any programs, for even the desktop etc. to load. It would work if it was the only choice, but not ideal. So I needed a new SSD and went on the hunt this morning, to see what I could find.

1Tb is adequate as I have a 1Tb internal flash blade in the iMac and am duplicating that. If I could afford a 2Tb, I’d buy one. But times are hard and the price difference is considerable. But it’s always worth looking around for offers. In the end it came down to three possible drives. The Samsung T5 1Tb, Samsung T7 1Tb or Sandisk Extreme 1Tb

I opted for the Samsung T7 1Tb. It was £142 from Ebuyer. The main deciding factor for me was for £20 extra above the Sandisk, the T7 runs at twice the speed – 1050 Mbs, compared to 550 Mbs of the other two.

At time of writing:

Sandisk £120 550Mbs
Samsung T5 £130 550Mbs
Samsung T7 £142 1050Mbs

Let me know how you get on in the comments. I’d love to hear your feedback.

My new Samsung T7 drive just arrive. It’s teeny tiny….

Samsung T7 size

Setting Up an Automated Nightly Backup

Follow this guide to set up Automated Nightly Backups

Want to know more about setting up a bomb proof backup system for your computer – read more here on my Photographers Guide to Backup.

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