Which external hard drive: USB 3 or Thunderbolt?

If you’re backing up significant amounts of data to an external drive, choosing a device equipped with USB 3 or Thunderbolt can shave precious time from your transfers.

Which external hard drive: USB 3 or Thunderbolt?

USB has long been the industry standard for inter-device connectivity, and while USB 2’s speeds of 480Mbits/sec were surpassed by USB 3’s 4.8Gbits/sec, Intel’s Thunderbolt has claimed the lead by promising transfer speeds of up to 10Gbits/sec.

Currently, though, Thunderbolt is available on limited PCs, and only widely adopted by Apple’s recent iMacs and MacBooks, including the 21.5in iMac used for testing.

Even with a standard external HDD, the differences can be dramatic. LaCie’s Rugged drive is a portable device with a standard 1TB 2.5in HDD, and when connected to our iMac via USB 2, performance in the CrystalDiskMark benchmark was less than impressive.

This was especially noticeable while reading and writing larger files: the LaCie achieved a maximum transfer speed of 42MB/sec. Moving to a USB 3 or Thunderbolt connection almost tripled that figure: speeds increased to 116MB/sec – the maximum you can expect from a standard laptop HDD.

In our real-world tests, the benefits of the faster interfaces remain obvious. Opening images in Photoshop from the external drive took half the time with USB 3 or Thunderbolt, with 1GB of images loading in only 19 seconds – via USB 2, we were kept waiting for 46 seconds. Backing up a 5GB folder filled with a mixture of file sizes took more than four minutes over USB 2; switching to USB 3 or Thunderbolt slashed that to less than two minutes.

Faster drives

Very few devices are capable of pushing USB 3 or Thunderbolt to their limits. While USB 3’s theoretical 4.8Gbits/sec bandwidth translates into a potential throughput of 612MB/sec, Thunderbolt’s claimed 10Gbits/sec promises transfer speeds of up to 1,280MB/sec – way beyond the capability of even the fastest SSDs.

If speed is of the essence, it might be worth considering an external drive that uses single or multiple SSDs. We tested Thunderbolt with LaCie’s Thunderbolt-equipped Little Big Disk, which features two 120GB SSDs in a striped RAID0 array.

For large files, Thunderbolt posted read speeds four times faster than what it managed with the HDD, with significant improvement in small-file transfer speeds, too.

Loading our test Crysis level took only 34 seconds – half as long as with the HDD – while opening 1GB of photos in Photoshop was seven seconds faster, taking only 12 seconds. Backing up a 5GB folder of photos took 1min 32secs from the iMac’s HDD, only a little quicker than with the LaCie Rugged drive.

The iMac’s HDD is the limiting factor here – when we retested from a RAM disk, the LaCie backed up the 5GB folder in a mere 26 seconds. Unless your main system drive is an SSD, writing files to a superfast external disk or RAID array will be limited to the speed of the slowest device in the chain.


If you’re planning on buying an affordable external HDD, moving from USB 2 to USB 3 will bring noticeable improvement, especially if you’re backing up larger files, such as movies, music and photos. Moving from USB 3 to Thunderbolt won’t have much of an impact, however, and certainly not until you pay a premium for SSD-equipped devices or spend megabucks on high-end disk arrays.

In either case, we’d think long and hard before splashing out serious money: unless you’re an avid video producer who needs terabytes of data on a permanent high-speed link, or are planning to offload your games collection entirely to an external drive and can’t wait a few extra seconds for games to load, we’d stick with the cheaper HDD-based devices.

And if you already have an HDD or two lying around, save your pennies and buy a USB 3 hard drive caddy – it’s a cheap and easy way to turn an old HDD into a high-speed external drive.

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