4 reasons you should use an external SSD as your Mac's boot drive
Many of the most important devices in our lives feature non-upgradeable storage, from phones to select laptops and desktop computers, which introduces new problems. When you run out of storage space, your system can start to slow down, and you might not be able to install new apps or download important files. Considering these limitations, you may feel like you need to buy a new computer when your disk space runs out. That's especially true for owners of modern Intel and Apple silicon Macs, which feature flash chips that are soldered to the logic board. For macOS users, the days of swapping out a hard drive or SSD are over.
However, I think one of the biggest tech mistakes you can make is to buy a new computer when all you need is more storage space. It's true that it's incredibly difficult to add more storage to a Mac with a soldered SSD, but there are ways you can get creative. Now that external drives with Thunderbolt 4 support are faster than ever, using an external boot drive for your Mac makes a lot of sense. It'll allow you to expand your Mac's available storage without needing to buy a new one altogether. Plus, for casual users, it's a more simplistic solution than a dual-drive workflow would be.
Here's the case for making your macOS startup disk an external drive rather than shelling out a lump sum for a new Mac.
It's simpler
Casual users don't want to manage a dual-drive setup
First, let's address the elephant in the room. If you have the ability to, you should not use an external SSD as an alternative to your Mac's boot drive. An external drive would work better in tandem with your macOS startup disk. You could have your operating system on your computer's inbuilt SSD for the best performance, and then have a separate external SSD for additional files, apps, and more. The benefit for keeping your internal SSD in use is that you can make use of swap memory on Apple silicon systems. Essentially, free SSD space can be used as virtual RAM to give you extra memory when you need it.
With that being said, I recognize that casual users may not want to fiddle with the complicated setup of using multiple storage devices. To tech enthusiasts, managing multiple storage locations — or even a NAS — might not be that tricky. But after years of serving as free tech support for friends and family that aren't as tech-inclined, I can confidently say that simply using two SSDs is enough to frustrate some average consumers. Another thing to consider is that for users of Macs with a spinning hard drive, an external SSD will likely be faster than a disk boot drive.
While I think a NAS is incredibly useful and everyone should have one if they can, that doesn't mean you need one.
In many instances, the choice isn't between using an inbuilt SSD as a boot drive and an external drive or moving over to an external boot drive altogether. It's between using a boot drive with more storage or buying a new computer. And in that case, an external boot drive is certainly the way to go.
Accessories are here to help
You can make an external SSD feel like an internal one
When many people think of external drives, an image of a dangling SSD connected by a long USB cable probably comes to mind. For Mac users, that doesn't have to be the reality of using an external SSD as your boot drive. There are quite a few excellent SSD enclosures that will blend into your setup nicely and cleverly disguise your storage device. Two of the best ones are from Satechi, and I've used the company's offerings for the Mac Mini, Mac Studio, and iMac. They're simple USB docks that look like they're made to be paired with your Mac, but they hide an inbuilt SSD enclosure. You can throw in an SSD, install macOS Sonoma on it, and forget about it. It's really that easy.
Satechi has been making stands and hubs for Mac computers for a while now, but this one represents the company's best work.
Thunderbolt SSDs are blazing fast
You might not notice the difference between using a TB4 boot drive and your internal SSD
An external SSD can certainly beat the speed of a Mac's internal hard drive, if it still has one. However, you may not know that the speeds of certain Thunderbolt 4 storage devices can actually be near the speed of certain soldered Mac SSDs. The maximum speed you can get from a Thunderbolt 4 SSD is 5,000MB/s, but that will probably be more like between 3,000MB/s and 4,000MB/s in real-world usage. That's pretty good, and it's certainly serviceable for a boot drive.
By comparison, the speed of a modern Mac's internal SSD will largely depend on how many NAND flash chips it uses. For example, base-model MacBook Air models (namely the M1 and M2 variants) have only featured a single NAND flash chips. In real-world performance, Macs with a single NAND chip will perform worse than Macs with multiple NAND chips. That's the difference between read/write speeds in the 1,000s and 2,000s of megabytes per second and speeds in the 5,000s and 6,000s of megabytes per second. So yes, the right external drive can be fast enough to serve as a startup disk, and it might even be faster than your internal SSD.
Samsung's T9 Portable SSD is excellent for storing all types of files, but it comes in handy as a 4K ProRes-capable drive for the iPhone 15 Pro.
It's a great way to 'upgrade' your Mac
If you own a Mac with a soldered SSD, this may be your only option
This kind of extensive Mac upgrade is a thing of the past on modern Apple silicon computers.
Again, I want to emphasize that external drives aren't always the best solution. Sometimes, they're the only solution. There are some older Macs that are capable of receiving storage upgrades — if you still have a Mac Pro or an iMac from the early-to-mid 2010s, you should certainly explore that option — but many can't. With new Apple silicon Macs, the storage you buy from day one is the storage you're stuck with. I'm extremely concerned that these Macs will end up in the landfill way sooner than they should simply because users run out of storage. Using an external SSD as your Mac's boot drive will keep your computer up-and-running for longer without drastically changing the everyday experience of using the machine.
I'm really going to miss upgradeability
The pros and cons of using an external boot drive
Employing an external SSD as your Mac's startup disk is a much better alternative to buying an entirely new computer. Simply needing more storage and not being able to upgrade your SSD shouldn't be the only reason you cast your current Mac aside. However, there are real pros and cons to consider. The benefits include low-cost upgrades, the ability to hot-swap SSDs between Macs, and a streamlined experience. On the other hand, you do lose some performance by going with an external SSD as your main OS drive in some cases. But when the choice is between buying a new Mac and using an external boot drive, I think there's an easy answer.