The Right Connections
Buying an external hard drive for your Mac is not all that different from buying one for your Windows PC, except for one very important conundrum: Newer MacBooks and MacBook Pros only come with Thunderbolt 3 ports, but the arrival of Thunderbolt 3-equipped drives has come in the form of a trickle, rather than a flood. Most of the current models are designed for photographers and video editors who need to store mountains of footage and access it very quickly. As a result, they are typically SSDs or RAID arrays, which means they're also very expensive. So what's a Mac user who just wants to backup his or her files using Time Machine to do? Read on as we answer that question, along with all of your other Mac external storage quandaries.
A New File System
Thunderbolt 3 and USB-C are the latest innovations in the external storage market, but before we get to them, we need to address a basic building block of hard drives that has always affected compatibility, and probably always will: the file system. An external drive's file system is the most important factor that determines whether or not it's readable by Macs, PCs, or both. Since the late 1990s, Apple has used the Mac OS Extended file system, commonly abbreviated as HFS+, to power its laptop and desktop computers. But this year, with the release of the macOS High Sierra operating system, Cupertino switched to an entirely new file format. It's simply called the Apple File System, and it's the first format to be used on Apple computers as well as the iOS ecosystem of iPads, iPhones, iPods, the Apple TV, and the Apple Watch.
There are many benefits to switching from HFS+ to the Apple File System, including better security thanks to native encryption, but the most important thing to note for external drive shoppers is that it's backward-compatible. In other words, any drive formatted with HFS+ (which includes most Mac-specific drives on the market today) will work just fine with a Mac that's running macOS High Sierra.
Neither Apple File System nor HFS+ works with Windows, however. If you plan to use your external drive with computers that run both operating systems, you should consider a drive formatted with the exFAT file system. Microsoft introduced exFAT about a decade ago, which means that it's still relatively young as far as file systems go. You won't get the security and efficiency of Apple File System, but you will get the convenience of being able to transfer files back and forth between Windows and macOS simply by plugging in and unplugging your drive.
Finally, note that you can easily reformat almost any drive you buy, so you're not limited to buying only those intended for use with Macs. If you really fancy a drive formatted for Windows (usually in the NTFS format), you can use the Disk Utility in macOS to reformat it after you bring it home from the store. There are a few exceptions to this rule, but they're rare. The only drive we've tested recently that isn't Mac-compatible even if it's formatted is the pro-oriented Akitio Thunder3 PCIe SSD, which uses a lightning-quick Intel SSD with firmware that requires Intel motherboards that aren't found in any Mac computers.
SSD vs. Spinning Drive
Once you've settled on a file system, you then have to determine which storage medium you want: solid state or spinning disk. Each has its advantages and disadvantages, and unfortunately—unlike the file system—the type you buy is the type you're stuck with for the life of the drive. A solid-state drive, or SSD, offers quick access to your data because it stores them in a type of flash memory rather than on spinning platters. SSDs are often smaller and lighter than spinning external drives as well, which is also thanks to the lack of moving parts. Their small size means they can often fit into a pants or jacket pocket, which makes them a better choice if you're looking for a portable external drive that you'll be carrying with you frequently. One major downside, however, is that they're much more expensive. You could pay more than 30 cents per gigabyte for an SSD, while spinning drives can be had for less than 10 cents per gigabyte—often much less. External SSDs also have much less capacity, with most drives topping out at 2TB. Compare that with spinning drives, which are not hard to find in capacities upwards of 8TB.
For professional videographers who edit lots of 4K footage and gamers or movie buffs who have large libraries of multi-gigabyte titles, an external RAID array is worth considering, since it combines the speed of an SSD with the gargantuan capacities of a spinning drive. An array typically contains as few as two or as many as eight spinning drives, which all work together to both speed up throughput and guard your precious files against corruption if one of the drives fail. The result is that you can get SSD-like speeds, with data throughput of more than 400MBps, and capacities that top out close to 50TB. You'll pay handsomely, of course. The Mac-specific Promise Pegasus3 can cost as much as $5,000.
On the other hand, if you're looking to buy an external drive mainly to back up your files (which you should definitely do) and it will rarely leave your home office, an inexpensive spinning drive will work just fine.
Searching for Thunderbolt 3
So faster, smaller (both physically and in terms of gigabytes) drives come at a premium, while spinning drives offer a much better value while sacrificing speed. But what happens when you throw yet another variable into the mix: the connection between your drive and your Mac? As you might have guessed, the answer is more tradeoffs. Every Mac laptop sold today comes with USB-C ports that support Thunderbolt 3, but other than a headphone jack, they are the only connectivity options available, which means you'll need need an adapter to plug in any device that doesn't have a USB-C cable. Fortunately, Thunderbolt 3 via USB-C supports blazing throughput of 40Gbps, double the speed of the old Thunderbolt 2 standard and many times the 5GBps that USB 3.0 offers. Unfortunately, you won't find many Thunderbolt 3-compatible drives on the market currently. Even some Mac-specific drives are still sold with USB 3.0 connectors. Moreover, the Thunderbolt 3 drives you can buy are constrained by the maximum throughput of the drive itself, rather than the Thunderbolt 3 interface. The speediest SSDs we've tested recently top out at around 600MBps, for instance.
This means that for now, it's best to include Thunderbolt 3 support in your buying decision only if you're concerned about futureproofing. While it's nice of manufacturers to include a USB-C cable for people who own a USB-C-only MacBook, you can pick up a converter for a few dollars online if the drive you're eyeing doesn't offer one. Meanwhile, iMacs, Mac Pros, and Mac Minis all still come with USB 3.0 ports, so they won't require adapters, for now.
Drives intended for PCs sometimes come bundled with software that will automatically back up your files to the drive when it's connected, but such software isn't really a consideration for Mac users, who already have an excellent built-in backup option in the form of Time Machine. The first time you plug in an external drive, Time Machine will ask if you want to use it as a backup drive. While you can customize backup options in System Preferences, such as asking Time Machine to exclude certain folders, there's no action required on your part if you're happy with the default settings. The next time you plug in your drive, Time Machine will automatically set to work creating a backup.
Unless your drive is never going to leave your home or office, you should also consider its physical durability. Rugged, waterproof drives are a good option not just for surfers and BMX riders, as their marketing seems to suggest, but also for people who are carrying their drives to and from school or work, where they might occasionally get spilled on or dropped on the floor.
Finally, you might want to consider how the drive will look when it's plugged into your Mac. Some drives, like the Western Digital My Book, come in a variety of colors. Many others feature copious amounts of aluminium and industrial-chic styling to match the design cues of your MacBook or iMac.
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